ISWI  ( I mitation  SWI tch) is one of the five major DNA chromatin remodeling complex types, or subfamilies, found in most eukaryotic organisms. [ 1 ]   ISWI remodeling complexes place nucleosomes along segments of DNA at regular intervals. The placement of nucleosomes by ISWI protein complexes typically results in the silencing of the DNA because the nucleosome placement prevents transcription of the DNA.  [ 2 ]   ISWI, like the closely related SWI/SNF subfamily, is an ATP-dependent chromatin remodeler.  However, the chromatin remodeling activities of ISWI and SWI/SNF are distinct and mediate the binding of non-overlapping sets of DNA transcription factors. [ 3 ]


The protein ISW1 is the first  ATPase   subunit  which has been isolated in the ISWI  chromatin   remodeling  family in the fruit fly  Drosophila .  This protein presents high level of similarity to the  SWI/SNF  chromatin remodeling family in the ATPase domain. Outside the ATPase domain ISWI loses the similarity with the member of the SWI/SNF family, possessing a  SANT domain  instead of the  bromodomain . The protein ISWI can interact with several proteins giving three different chromatin-remodeling complexes in  Drosophila melanogaster :  NURF  ( nucleosome  remodeling factor), CHRAC (chromatin remodeling and assembly complex) and ACF (ATP-utilising chromatin remodeling and assembly factor).


In vitro , the ISWI protein alone can assemble nucleosomes on linear DNA and it can move nucleosomes on linear DNA from the center to the extremities. Inside the CHRAC complex, ISWI catalyzes the inverse reaction, moving nucleosomes from the extremities to the center. [ 4 ]


A single molecule study using  atomic force microscopy  (AFM) and  tethered particle motion  (TPM) has observed that ISWI can bind naked DNA in the absence of  ATP , wrapping DNA around the protein. In presence of  ATP , the protein generates DNA loops while simultaneously generating negative  supercoils  in the template. [ 5 ]  The first figure in this paper shows three AFM images from where single DNA interacting with ISWI was deposed on mica surfaces. On the center, a single ISWI is bound near the end of a dsDNA template. The right image shows two DNA loops generated by ISWI. These loops contains supercoils.
The TPM study instead showed that the duration of loop formed by ISWI was ATP-dependent.


In  molecular biology ,  insertional mutagenesis  is the creation of  mutations  in DNA by the addition of one or more  base pairs . Such insertional mutations can occur naturally, mediated by  viruses  or  transposons , or can be artificially created for research purposes in the lab.


This is a technique used to study the function of  genes . A  transposon  such as the  P element  of  Drosophila melanogaster  is allowed to integrate at random locations in the  genome  of the organism being studied. Mutants generated by this method are then screened for any unusual  phenotypes . If such a phenotype is found then it can be assumed that the insertion has caused the gene relating to the usual phenotype to be inactivated. Because the sequence of the transposon is known, the gene can be identified, either by sequencing the whole genome and searching for the sequence, or by using the  polymerase chain reaction  to amplify specifically that gene.


Because many viruses integrate their own genomes into the genomes of their host cells in order to replicate, mutagenesis caused by viral infections is a fairly common occurrence. Not all integrating viruses cause insertional mutagenesis, however.


Some DNA insertions will lead to no noticeable mutation. Historically, lentiviral vectors included strong viral promoters which had a side effect of insertional mutagenesis, nuclear DNA mutations that effect the function of a gene. [ 1 ]  These strong viral promotors were shown to be the main cause of  cancer formation . [ 1 ]  As a result, viral promotors have been replaced by cellular promotors and regulatory sequences. [ 1 ]   For those viruses such as  gammaretroviruses  that tend to integrate their DNA in genetically unfavorable locations, the severity of any ensuing mutation depends entirely on the location within the host's genome wherein the viral DNA is inserted.  If the DNA is inserted into the middle of an essential gene, the effects on the cell will be drastic. Additionally, insertion into a gene's  promoter region  can have equally drastic effects.  Likewise, if the viral DNA is inserted into a  repressor , the promoter's corresponding gene may be over-expressed – leading to an overabundance of its product and altered cellular activity.  If the DNA is inserted into a gene's  enhancer region , the gene may be under-expressed – leading to a relative absence of its product, which can significantly interrupt the activity of the cell.


Alteration of different genes will have varying effects on the cell.  Not all mutations will significantly affect the proliferation of the cell.  However, if the insertion occurs in an essential gene or a gene that is involved in  cellular replication  or  programmed cell death , the insertion may compromise the viability of the cell or even cause the cell to replicate interminably – leading to the formation of a tumor, which may become cancerous.


Insertional mutagenesis is possible whether the virus is of the self-inactivating types commonly used in gene therapy or competent to replicate. The virus inserts a gene (known as a viral oncogene) normally near the cellular myc (c-myc)gene. The  c-myc  gene is normally turned off in the cell; however when it is turned on it is able to push the cell into the  G1 phase  of the  cell cycle  and cause the cell to begin replication, causing unchecked cell proliferation while allowing the viral gene to be replicated. After many replications where the viral gene stays latent tumours begin to grow. These tumours are normally derived from one mutated/ transformed  cell (clonal in origin).  Avian leukosis virus  is an example of a virus that causes disease by insertional mutagenesis. Newly hatched chicks infected with the Avian leukosis virus will begin to form tumours that will begin to appear in their  bursa of Fabricius  (like the human thymus). This viral gene insertion is also known as a promoter insertion as it drives the expression of the c-myc gene. There is an example of an insertional mutagenesis event caused by a  retrotransposon  in the human genome where it causes Fukuyama-type muscular dystrophy. [ 2 ]


Insertional inactivation  is a technique used in  recombinant DNA  engineering where a plasmid (such as  pBR322 ) [ 3 ]  is used to disable the expression of a gene. [ 4 ]


The inactivation of a gene by inserting a fragment of DNA into the middle of its coding sequence. Any future products from the inactivated gene will not work because of the extra codes added to it. An example is the use of pBR322, which has genes that respectively encode polypeptides that confer resistance to ampicillin and tetracyclin antibiotics. Hence, when a genetic region is interrupted by the integration of pBR322, the gene function is lost but new gene function (resistance to specific antibiotics) is gained.


An alternative strategy for insertional mutagenesis has been used in vertebrate animals to find genes that cause cancer. In this case a transposon, e.g.  Sleeping Beauty , is designed to interrupt a gene in such a way that it causes maximal genetic havoc. Specifically, the transposon contains signals to truncate the expression of an interrupted gene at the site of the insertion and then restart the expression of a second truncated gene. This method has been used to identify  oncogenes . [ 5 ] [ 6 ]


Integrative and conjugative elements  ( ICEs ) are  mobile genetic elements  present in both  gram-positive  and  gram-negative   bacteria . In a donor cell, ICEs are located primarily on the  chromosome , but have the ability to excise themselves from the genome and transfer to recipient cells via  bacterial conjugation .


Due to their physical association with chromosomes, identifying integrative and conjugative elements has proven challenging, but  in silico  analysis of bacterial genomes indicate these elements are widespread among many microorganisms. [ 1 ] [ 2 ]


ICEs have been detected in  Pseudomonadota  (e.g.,  Pseudomonas  spp.,  Aeromonas  spp.,  E. coli ,  Haemophilus  spp.),  Actinomycetota  and  Bacillota . Among many other virulence determinants, ICEs may spread antibiotic and metal ion resistance genes across prokaryotic phyla. [ 1 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ]  In addition, ICE elements may also facilitate the mobilisation of other DNA modules such as  genomic islands . [ 3 ] [ 7 ]


Although ICEs exhibit various mechanisms promoting their integration, transfer and regulation, they share many common characteristics. ICEs comprise all mobile genetic elements with self-replication, integration, and conjugation abilities, including conjugative transposons, regardless of the particular conjugation and integration mechanism by which they act. Some immobile genomic  pathogenicity islands  are also believed to be defective ICEs that have lost their ability to conjugate.


ICEs combine certain features of the following mobile genetic elements: [ 1 ]


In contrast to plasmids and phages, integrative and conjugative elements cannot remain in an extrachromosomal form in the cytoplasm of bacterial cells and  replicate only with the chromosome they reside in.


ICEs possess the structure organized into three gene modules that are responsible for their integration with the chromosome, excision from the genome and conjugation, as well as regulatory genes. [ 1 ] [ 3 ]  All integrative and conjugative elements encode integrases that are essential for controlling the excision, transfer and integration of an ICE. The representative example of ICE integrases is the integrase encoded by lambda phage. The transfer of an integrated ICE element from the donor to recipient bacterium must be preceded by its excision from the chromosome that is co-promoted by small  DNA-binding proteins , the so-called recombination directionality factors. The dynamics of the integration and excision processes are specific to each integrative and conjugative element. [ 1 ]


Interlocus contest evolution  (ICE) is a process of intergenomic conflict by which different  loci  within a single  genome  antagonistically  coevolve . ICE supposes that the  Red Queen process , which is characterized by a never-ending antagonistic  evolutionary arms race , does not only apply to  species  but also to  genes  within the genome of a species. [ 1 ]


Because  sexual recombination  allows different gene loci to evolve semi-autonomously, genes have the potential to coevolve antagonistically. ICE occurs when "an allelic substitution at one locus selects for a new allele at the interacting locus, and vice versa." As a result, ICE can lead to a chain reaction of perpetual gene substitution at antagonistically interacting loci, and no stable equilibrium can be achieved. The rate of evolution thus increases at that locus. [ 1 ]


ICE is thought to be the dominant mode of evolution for genes controlling social behavior. [ 1 ]  The ICE process can explain many biological phenomena, including intersexual conflict,  parent offspring conflict , and interference competition.


A fundamental conflict between the sexes lies in differences in investment: males generally invest predominantly in fertilization while females invest predominantly in offspring. [ 2 ]  This conflict manifests itself in many traits associated with  sexual reproduction . Genes expressed in only one sex are selectively neutral in the other sex; male- and female-linked genes can therefore be acted upon separated by selection and will evolve semi-autonomously. [ 1 ]  Thus, one sex of a species may evolve to better itself rather than better the species as a whole, sometimes with negative results for the opposite sex: loci will antagonistically coevolve to enhance male reproductive success at females’ expense on the one hand, and to enhance female resistance to male coercion on the other. [ 3 ]  This is an example of  intralocus sexual conflict , and is unlikely to be resolved fully throughout the genome. However, in some cases this conflict may be resolved by the restriction of the gene’s expression to only the sex that it benefits, resulting in  sexual dimorphism . [ 4 ]


The ICE theory can explain the differentiation of the human  X-  and  Y-chromosomes . Semi-autonomous evolution may have promoted genes beneficial to females in the X-chromosome even when detrimental to males, and genes beneficial to males in the Y-chromosome, even when detrimental to females. As the distribution of the X-chromosome is three times as large as the Y-chromosome (the X-chromosome occurs in 3/4 of offspring genes, while the Y-chromosome occurs in only 1/4), the Y-chromosome has a reduced opportunity for rapid evolution. Thus, the Y-chromosome has "shed" its genes to leave only the essential ones (such as the  SRY gene ), which gives rise to the differences in the X- and Y-chromosomes. [ 5 ]


A father, mother and offspring may differ in the optimal resource allocation to the offspring. This co-evolutionary conflict can be considered in the context of ICE. Selection will favor genes in the male to maximize female investment in the current offspring, no matter the consequences to the female's reproduction later in life, while selection will favor genes in the female that increase her overall lifetime  fitness . Genes expressed in the offspring will be selected to produce an intermediary level of resource allocation between the male-benefit and female-benefit loci. This three-way conflict again occurs when parents feed their offspring, as the optimum feeding rate and optimum point in time to discontinue feeding differ between father, mother and offspring. [ 1 ]


ICE can also explain the theory of  interference competition , which is most likely to be associated with opposing sets of genes that determine the outcome of  competition  between individuals. Different sets of genes may code for signal or receiver  phenotypes , such as in the context of  threat displays : when a competing male can win more contests by intimidation, rather than by fighting, selection will favor the accumulation of deceitful genes that may not be honest indicators of the male’s fighting capability. [ 1 ]


For example, primitive male  elephant seals  may have used the lowest frequencies in the threat call of a rival as an indication of body size. The elephant seal's enormous nose may have evolved as a  resonating device  to amplify low frequencies, [ 6 ]  illustrating selection that favors the production of low-frequency threat vocalizations. However, this counter-selects for receptor systems that provide an increased threshold required for intimidation, which in turn selects for deeper threat vocalizations. The rapid divergence of threat displays among closely related species provides further evidence in support of the co-evolutionary arms race within the genome of a single species, driven by the ICE process. [ 1 ]


Island Conservation  is a  non-profit organization  with the mission to "restore islands for nature and people worldwide" and has therefore focused its efforts on islands with species categorized as  Critically Endangered  and  Endangered  on the  IUCN's Red List . [ 4 ]  Working in partnership with local communities, government management agencies, and conservation organizations, Island Conservation develops plans and implements the removal of invasive alien species, [ 5 ]  and conducts field research to document the benefits of the work and to inform future projects.


Island Conservation's approach is now being shown to have a wider beneficial effect on the marine systems surrounding its project areas. [ 6 ] [ 7 ] [ 8 ]  In addition, invasive vertebrate eradication has now been shown to have many benefits besides conservation of species. Specifically, the approach has been found to align with 13 UN  Sustainable Development Goals  and 42 associated targets encompassing marine and terrestrial biodiversity conservation, promotion of local and global partnerships, economic development,  climate change mitigation , human health and sanitation and sustainable production and consumption. [ 9 ] [ 10 ]


To date Island Conservation has deployed teams to protect 1,195 populations of 487 species and subspecies on 64 islands. [ 11 ]


The work of Island Conservation is not without controversy, This is documented in the book  Battle at the End of Eden . [ 12 ]  Restoring islands requires removing whole populations of an invasive species. There is an ethical question of whether humankind has the right to remove one species to save others. However, a 2019 study suggests that if eradications of invasive animals were conducted on just 169 islands, the survival prospects of 9.4% of the Earth's most highly threatened terrestrial insular vertebrates would be improved. [ 13 ] [ 14 ]


Island Conservation was founded by Bernie Tershy and Don Croll, both Professors at  UCSC's   Long Marine Lab . These scientists learned about the story of  Clipperton Island  which had been visited by ornithologist Ken Stager of the  Los Angeles County Museum  in 1958. Appalled at the depredations visited by  feral pigs  upon the island's  brown booby  and  masked booby  colonies (reduced to 500 and 150 birds, respectively), Stager procured a shotgun and removed all 58 pigs. By 2003, the colonies numbered 25,000 brown boobies and 112,000 masked boobies, the world's second-largest brown booby colony and largest masked booby colony. [ 15 ]


Much of organization's early focus was working in Mexico in conjunction with its sister organization, Grupo de Ecología y Conservación de Islas, in the  Gulf of California  and off the Pacific Coast. [ 16 ] [ 17 ]   Subsequently, Island Conservation expanded its geographic scope to the  Channel Islands of California ,  Pacific Coast of Canada ,  The Aleutians Islands ,  Hawaiian Islands , and finally to the  Pacific ,  Caribbean , and  South America .


Island Conservation has a strong scientific grounding. Over 160 peer-reviewed publications in major journals such as  Biological Conservation ,  Conservation Biology  and  Proceedings of the National Academy of Sciences  have been authored or co-authored by Island Conservation staff and contractors. [ 18 ]


As Island Conservation does not have management responsibility over any islands itself, all projects are in partnership with the island owner/manager, island users, local communities and regulatory authorities. Since its founding in 1994, the organization has developed partnerships with over 100 organizations. [ 19 ]  Partners include conservation organizations, government agencies, regulatory agencies, scientific institutions, and international conservation consortiums. Island Conservation is a member of the  International Union for Conservation of Nature (IUCN) ,  Alliance for Zero Extinction , [ 20 ]  and has a  Memorandum of Understanding  with the  US Fish & Wildlife Service , [ 21 ]  and  BirdLife International , [ 22 ]  amongst others.


The organization's founding advisory board [ 23 ]  is composed of prominent scientists, practitioners, and authors in the fields of conservation biology and invasive species including  Paul Ehrlich , José Sarukhán Kermez,  Russell Mittermeier ,  Harold Mooney ,  David Quammen ,  Peter Raven ,  Michael Soulé , and  Edward O. Wilson .


In this region, Island Conservation currently works in  the United States  and  Canada . In the United States, the  Anacapa Island  Restoration Project [ 24 ] [ 25 ] [ 26 ]  was completed in 2002 and benefited the  Scripps's murrelet ,  Cassin's auklet , and Anacapa Deer Mouse. The  Lehua Island  Restoration Project was completed in 2006 which benefited  Newell's shearwater  and  black-footed albatross . [ 27 ] [ 28 ]  Subsequently, projects completed include the  Hawadax Island  Restoration Project [ 29 ] [ 30 ] [ 31 ]  in 2008, the San Nicolas Island Project [ 32 ] [ 33 ] [ 34 ]  in 2010, and the  Palmyra Island  Restoration Project [ 35 ]  in 2011.


Key federal government partnerships in North America include in the  US Department of Interior ,  USFWS ,  NPS , the  US Department of Agriculture-APHIS , National Wildlife Research Center,  NOAA ,  Parks Canada Agency , and  Environment and Climate Change Canada .  Island Conservation is working with the following non-governmental organizations:  Coastal Conservation Association (CA) ,  Bird Studies Canada ,  American Bird Conservancy ,  The Nature Conservancy , and Grupo de Ecología y Conservación de Islas.


Since 2010, Island Conservation has contributed to the development and implementation of island restoration projects in  Australia  ( Lord Howe Island [ 36 ]   and  Norfolk Island ),  French Polynesia  ( Tetiꞌaroa  Restoration Project in 2022, [ 37 ]  Acteon-Gambier Archipelago Restoration Project [ 38 ]  in 2015),  Tonga  ( Late Island  and numerous small islets),  Republic of Palau  (including within the  Rock Islands Southern Lagoon World Heritage Area [ 39 ] ),  Federated States of Micronesia  (Ulithi Lagoon), and  New Caledonia  (Walpole Island). Island Conservation is an active member of the Pacific Invasives Partnership. [ 40 ]  Other key partnerships include Invasive Species Council, [ 41 ]   BirdLife International ,  New Zealand Department of Conservation ,  SPREP  and the  Ornithological Society of French Polynesia .


In this region, Island Conservation works primarily in  Puerto Rico ,  The Commonwealth of The Bahamas , and the  Dominican Republic . In May 2012, Island Conservation and the  Bahamas National Trust  worked together to remove invasive house mice from Allen Cay to protect native species including the  Allen Cays rock iguana  and  Audubon's shearwater . [ 42 ]  Since 2008, Island Conservation and the  US Fish and Wildlife Service  (USFWS) have worked together to remove invasive vertebrates from  Desecheo National Wildlife Refuge  in Puerto Rico, primarily benefiting the  Higo Chumbo cactus , three endemic reptiles, two endemic invertebrates, and to recover globally significant seabird colonies of  brown boobies ,  red footed boobies , and  bridled terns . [ 43 ]  Future work will focus on important seabird populations, key reptile groups including West Indian Rock Iguanas, and the restoration of  Mona Island , [ 44 ]  Alto Velo, and offshore cays in the Puerto Rican Bank and The Bahamas. Key partnerships include the USFWS,  Puerto Rico DNER , the  Bahamas National Trust , and the  Dominican Republic Ministry of Environment and Natural Resources .


In this region, Island Conservation works primarily in  Ecuador  and  Chile . In Ecuador, the  Rábida Island  Restoration Project was completed in 2010. A gecko (Phyllodactylus sp.) found during monitoring in late 2012 was only recorded from subfossils estimated at more than 5,700 years old. Live Rábida Island endemic land snails (Bulimulus (Naesiotus) rabidensis), not seen since collected over 100 years ago, were also collected in late 2012. [ 45 ]  This was followed in 2012 by the  Pinzon  and  Plaza Sur Island  Restoration Project primarily benefiting the  Pinzón giant tortoise ,  Opuntia galapageia ,  Galápagos land iguana . As a result of the project, Pinzon Giant Tortoise hatched from eggs and were surviving in the wild for the first time in more than 150 years [ 46 ] [ 47 ] [ 48 ] [ 49 ]
In 2019, The Directorate of Galápagos National Park with Island Conservation used drones to eradicate invasive rats from  North Seymour Island  - this was the first time such an approach has been used on vertebrates in the wild.  The expectation is that this innovation will pave the way for cheaper invasive species eradications in the future on small and mid-sized islands. [ 50 ] [ 51 ]
 [ 52 ] [ 53 ]  The current focus in Ecuador is  Floreana Island  with 55 IUCN  threatened species  present and 13 extirpated species that could be reintroduced after invasive mammals are eradicated. Partners include:  The Leona M. and Harry B. Helmsley Charitable Trust , Ministry of Environment (Galápagos National Park Directorate, Galápagos Biosecurity Agency), the Ministry of Agriculture, the Floreana Parish Council and the Galapagos Government Council.


In 2009 Chile, Island Conservation initiated formal collaborations with  CONAF , the country's protected areas agency, to further restoration of islands under their administration. In January 2014, the Choros Island Restoration Project was completed benefiting the  Humboldt penguin ,  Peruvian diving petrel , and the local eco-tourism industry. [ 54 ] [ 55 ]  The focus of future work includes the  Humboldt Penguin National Reserve  and the  Juan Fernández Archipelago , where technology developed by  Wildlife Drones  is being used to support conservation efforts. This includes tracking endangered species and collecting ecological data across challenging terrains.


From its earliest days, Island Conservation has prided itself on innovating its tools and approach to eradication projects.  Island Conservation implemented its first helicopter-based aerial broadcast eradication on Anacapa Island in 2001 refining technology developed in New Zealand for agriculture and pest control, this has been replicated on more than 10 international island restoration projects since. [ 56 ]  Island Conservation has developed practices for holding native species in captivity for re-release and mitigating risks to species, including the successful capture and release of endemic mice on Anacapa and hawks on Pinzon. [ 57 ]


In 2010, Island Conservation partnered with the U.S. Humane Society to remove feral cats from San Nicolas Island  [ 58 ]  for relocation to a sanctuary on the mainland California. New tools including a remote trap monitoring system, digital data collection system, [ 59 ]  and statistical decision support tools [ 60 ] [ 61 ]  improved the humanness of removal methods, reduced project cost, and reduced time to declare success. [ 62 ]


Following a series of failed eradication attempts in 2012, Island Conservation led a group of international experts to identify challenges on tropical islands [ 63 ]  resulting in recommend practices for tropical rodent eradications. [ 64 ]  Applying these lessons [ 65 ]  following a failed attempt on Desecheo island 2017 resulted in success.


Island Conservation led a horizon scan in 2015 [ 66 ]  that identified drones, [ 67 ]  genetic biocontrol, and conflict transformation as critical innovations to increase the scale, scope, and pace of rodent eradications. Since this exercise, Island Conservation formed the Genetic Biocontrol for Invasive Rodents (GBIRd) partnership to cautiously explore the development of safe and ethical genetic technologies [ 68 ]  to prevent extinctions, supported sustainable community-driven approaches [ 69 ]  to conservation projects, and implemented the world’s first drone-powered rat eradication.  The current focus of the Conservation Innovation program is to advance methods that increase safety, reduce cost, and improve the feasibility of eradicating invasive vertebrates from islands.


The  Jena Declaration  is a scientific statement that questions and refutes the concept of human " races in a biological sense ". It was published in September 2019 at the 112th Annual Meeting of the  German Zoological Society  (Deutsche Zoologische Gesellschaft) in Jena. The statement was written by leading scientists from the fields of  evolutionary research ,  genetics  and  zoology , and was instrumental in influencing the  legislative amendment  to remove the term "Rasse" (roughly "race in a biological sense") from the  German constitution . [ 1 ] [ 2 ] [ 3 ]  With this statement, the Institute for Zoology and Evolutionary Research at  Friedrich Schiller University Jena  explicitly distances itself from its 20th century predecessors, especially from the controversial scholar and evolutionary biologist  Ernst Haeckel , who was closely associated with the University of Jena and whose ideas of  racism  and  eugenics  are today considered scientifically untenable and morally reprehensible. [ 4 ]


The authors of the statement,  Martin S. Fischer ,  Uwe Hoßfeld ,  Johannes Krause  and  Stefan Richter  examined the issue of alleged human " races " from a  biological  perspective. They clarified that this concept has no  scientific  justification. Scientific studies of genetic variation within and between human populations showed that the biological concept of "race" was a typological construct based on arbitrarily selected physical  characteristics  and did not reflect the actual  genetic diversity  of the human species. [ 5 ]


The Jena Declaration affirms that there are no "races" in the biological sense in humans, since the genetic variation within human  populations  is often greater than the genetic variation between these populations. Only in  domestic animals  the  genetic similarity  within a breed is actually greater than between breeds. Moreover, genetic differences between populations are continuous, as humans  travelled  long before major explorations and voyages of conquest by Europeans, creating links between populations that were geographically distant from each other. External characteristics such as  skin colour , used for  typological classifications  or in everyday racism, are very superficial and rapidly changing  biological adaptations  to local conditions. In the human  genome , for example, there is not a single difference among the 3.2 billion base pairs that separates Africans from non-Africans. So not only is there not a single gene that accounts for "racial" differences, there is not even a single  base pair . [ 5 ]


The authors conclude that the concept of human "races" is the result of  racism  and not its precondition. Its use in scientific literature and social discourse often leads to misunderstandings and reinforces prejudice and discrimination. They therefore call for the term "race" to be discontinued in relation to people, except in  historical  or  socio-political  contexts where it should be understood as a  social construction  rather than a biological  reality . They argue that the use of the term in relation to people creates a false idea of genetically separate groups and that it is important to debunk this  myth  in order to combat racism.


They conclude the statement with an appeal to  educational institutions ,  media ,  authorities  and all  citizens  to reconsider the German term "Rasse" and emphasise genetic diversity and humanity instead of artificial and harmful categorisations.


In Germany, the Declaration had a considerable impact on public debate and  legislation , especially on the discussion about removing the term "Rasse" from the German constitution. [ 1 ] [ 3 ]


The Jena Declaration also led to a number of publications in the field of  education  and  learning . In the book "Den Begriff 'Rasse' überwinden: die 'Jenaer Erklärung' in der (Hoch-)Schulbildung" (Overcoming the Concept of Race: The Jena Declaration in (Higher) School Education), [ 6 ]  a variety of ideas and concepts for overcoming the concept of "race" are offered. In this publication, the Jena Declaration serves as an impulse for a nationwide reorientation of (high) school education. Another example is the publication "Die Jenaer Erklärung gegen Rassismus' und ihre Anwendung im Unterricht" (The Jena Declaration against Racism and its Application in the Classroom), [ 7 ]  which presents concrete examples of the application of the Jena Declaration in the classroom.


IQWiG (The independent Institute for Quality and Efficiency in Health Care) also backs the "Jena Declaration" by ceasing to translate the term "race" as "Rasse" in its evaluations. [ 8 ]


The Institute no longer translates the term "race" as "Rasse" in its assessments.


In  genetics , the  K a /K s  ratio , also known as  ω  or  d N / d S  ratio , [ a ]  is used to estimate the balance between  neutral mutations ,  purifying selection  and beneficial mutations acting on a set of  homologous protein-coding genes . It is calculated as the ratio of the number of  nonsynonymous substitutions  per non-synonymous site (K a ), in a given period of time, to the number of  synonymous substitutions  per synonymous site (K s ), in the same period. The latter are assumed to be neutral, so that the ratio indicates the net balance between deleterious and beneficial mutations. Values of K a /K s  significantly above 1 are unlikely to occur without at least some of the  mutations  being advantageous. If beneficial mutations are assumed to make little contribution, then K a /K s  estimates the degree of  evolutionary constraint .


Selection acts on variation in phenotypes, which are often the result of mutations in  protein -coding  genes . The  genetic code  is written in  DNA sequences  as  codons , groups of three  nucleotides . Each codon represents a single  amino acid  in a protein chain. However, there are more codons (64) than amino acids found in proteins (20), so many codons are effectively synonyms. For example, the DNA codons TTT and TTC both code for the amino acid  Phenylalanine , so a change from the third T to C makes no difference to the resulting protein. On the other hand, the codon GAG codes for  Glutamic acid  while the codon GTG codes for  Valine , so a change from the middle A to T does change the resulting protein, for better or (more likely) worse, [ b ]  so the change is not a synonym. These changes are illustrated in the tables below.


The K a /K s  ratio measures the relative rates of synonymous and nonsynonymous substitutions at a particular site.


Methods for estimating K a  and K s  use a  sequence alignment  of two or more nucleotide sequences of  homologous  genes that code for  proteins  (rather than being genetic switches, controlling development or the rate of activity of other genes). Methods can be classified into three groups: approximate methods,  maximum-likelihood methods , and counting methods.  However, unless the sequences to be compared are distantly related (in which case maximum-likelihood methods prevail), the class of method used makes a minimal impact on the results obtained; more important are the assumptions implicit in the chosen method. [ 1 ] : 498


Approximate methods involve three basic steps: (1) counting the number of synonymous and nonsynonymous sites in the two sequences, or estimating this number by multiplying the sequence length by the proportion of each class of substitution;
(2) counting the number of synonymous and nonsynonymous substitutions; and (3) correcting for multiple substitutions.


These steps, particularly the latter, require simplistic assumptions to be made if they are to be achieved computationally; for reasons discussed later, it is impossible to exactly determine the number of multiple substitutions. [ 1 ]


The maximum-likelihood approach uses  probability theory  to complete all three steps simultaneously. [ 1 ]   It estimates critical parameters, including the divergence between sequences and the transition/transversion ratio, by deducing the most likely values to produce the input data. [ 1 ]


In order to quantify the number of substitutions, one may reconstruct the ancestral sequence and record the inferred changes at sites (straight counting – likely to provide an underestimate); fitting the substitution rates at sites into predetermined categories ( Bayesian  approach; poor for small data sets); and generating an individual substitution rate for each  codon  (computationally expensive).  Given enough data, all three of these approaches will tend to the same result. [ 2 ]


The K a /K s  ratio is used to infer the direction and magnitude of  natural selection  acting on protein coding genes. A ratio greater than 1 implies positive or Darwinian selection (driving change); less than 1 implies purifying or stabilizing selection (acting against change); and a ratio of exactly 1 indicates neutral (i.e. no) selection. However, a combination of positive and purifying selection at different points within the gene or at different times along its evolution may cancel each other out. The resulting averaged value can mask the presence of one of the selections and lower the seeming magnitude of another selection.


Of course, it is necessary to perform a statistical analysis to determine whether a result is significantly different from 1, or whether any apparent difference may occur as a result of a limited data set.  The appropriate statistical test for an approximate method involves approximating dN − dS with a normal approximation, and determining whether 0 falls within the central region of the approximation.  More sophisticated likelihood techniques can be used to analyse the results of a Maximum Likelihood analysis, by performing a  chi-squared test  to distinguish between a null model (K a /K s  = 1) and the observed results. [ 1 ]


The K a /K s  ratio is a more powerful test of the neutral model of evolution than many others available in  population genetics  as it requires fewer assumptions. [ 1 ]


There is often a  systematic bias  in the frequency at which various  nucleotides  are swapped, as certain mutations are more probable than others. [ 1 ]   For instance, some lineages may swap C to T more frequently than they swap C to A.  In the case of the amino acid  Asparagine , which is coded by the codons AAT or AAC, a high C->T exchange rate will increase the proportion of synonymous substitutions at this codon, whereas a high C→A exchange rate will increase the rate of non-synonymous substitutions.  Because it is rather common for transitions (T↔C & A↔G) to be favoured over transversions (other changes), [ 1 ]  models must account for the possibility of non-homogeneous rates of exchange. [ 3 ]   Some simpler approximate methods, such as those of Miyata & Yasunaga and Nei & Gojobori, neglect to take these into account, which generates a faster computational time at the expense of accuracy; these methods will systematically overestimate N and underestimate S. [ 1 ]


Further, there may be a bias in which certain codons are preferred in a gene, as a certain combination of codons may improve translational efficiency. [ 1 ]   A 2022 study reported that synonymous mutations in representative yeast genes are mostly strongly non-neutral, which calls into question the assumptions underlying use of the K a /K s  ratio. [ 4 ]


In addition, as time progresses, it is possible for a site to undergo multiple modifications.  For instance, a codon may switch from AAA→AAC→AAT→AAA.  There is no way of detecting multiple substitutions at a single site, thus the estimate of the number of substitutions is always an underestimate.  In addition, in the example above two non-synonymous and one synonymous substitution occurred at the third site; however, because substitutions restored the original sequence, there is no evidence of any substitution.  As the divergence time between two sequences increases, so too does the amount of multiple substitutions.  Thus "long branches" in a dN/dS analysis can lead to underestimates of both dN and dS, and the longer the branch, the harder it is to correct for the introduced noise. [ 3 ]  Of course, the ancestral sequence is usually unknown, and two lineages being compared will have been evolving in parallel since their last common ancestor.  This effect can be mitigated by constructing the ancestral sequence; the accuracy of this sequence is enhanced by having a large number of sequences descended from that common ancestor to constrain its sequence by  phylogenetic  methods. [ 1 ]


Methods that account for biases in codon usage and transition/transversion rates are substantially more reliable than those that do not. [ 1 ]


Although the K a /K s  ratio is a good indicator of selective pressure at the sequence level, evolutionary change can often take place in the regulatory region of a gene which affects the level, timing or location of gene expression. K a /K s  analysis will not detect such change. It will only calculate selective pressure within protein coding regions.  In addition, selection that does not cause differences at an amino acid level—for instance,  balancing selection —cannot be detected by these techniques. [ 1 ]


Another issue is that heterogeneity within a gene can make a result hard to interpret. For example, if K a /K s  = 1, it could be due to relaxed selection, or to a chimera of positive and purifying selection at the locus. A solution to this limitation would be to apply K a /K s  analysis across many species at individual codons.


The K a /K s  method requires a rather strong signal in order to detect selection.
In order to detect selection between lineages, then the selection, averaged over all sites in the sequence, must produce a K a /K s  greater than one—quite a feat if regions of the gene are strongly conserved.
In order to detect selection at specific sites, then the K a /K s  ratio must be greater than one when averaged over all included  lineages  at that site—implying that the site must be under selective pressure in all sampled lineages.
This limitation can be moderated by allowing the K a /K s  rate to take multiple values across sites and across lineages; the inclusion of more lineages also increases the power of a sites-based approach. [ 1 ]


Further, the method lacks the capability to distinguish between positive and negative nonsynonymous substitutions.  Some  amino acids  are chemically similar to one another, whereas other substitutions may place an amino acid with wildly different properties to its precursor. In most situations, a smaller chemical change is more likely to allow the protein to continue to function, and a large chemical change is likely to disrupt the chemical structure and cause the protein to malfunction.  However, incorporating this into a model is not straightforward as the relationship between a nucleotide substitution and the effects of the modified chemical properties is very difficult to determine. [ 1 ]


An additional concern is that the effects of time must be incorporated into an analysis, if the lineages being compared are closely related; this is because it can take a number of generations for natural selection to "weed out" deleterious mutations from a population, especially if their effect on fitness is weak. [ 5 ] [ 6 ] [ 7 ] [ 8 ]  This limits the usefulness of the K a /K s  ratio for comparing closely related populations.


Additional information can be gleaned by determining the K a /K s  ratio at specific codons within a gene sequence.  For instance, the frequency-tuning region of an opsin may be under enhanced selective pressure when a species colonises and adapts to new environment, whereas the region responsible for initializing a nerve signal may be under purifying selection.  In order to detect such effects, one would ideally calculate the K a /K s  ratio at each site.  However this is computationally expensive and in practise, a number of K a /K s  classes are established, and each site is assigned to the best-fitting class. [ 1 ]


The first step in identifying whether positive selection acts on sites is to compare a test where the K a /K s  ratio is constrained to be < 1 in all sites to one where it may take any value, and see if permitting K a /K s  to exceed 1 in some sites improves the fit of the model.  If this is the case, then sites fitting into the class where K a /K s  > 1 are candidates to be experiencing positive selection.  This form of test can either identify sites that further laboratory research can examine to determine possible selective pressure; or, sites believed to have functional significance can be assigned into different K a /K s  classes before the model is run. [ 1 ]


The  Khmer people  ( Khmer :  ជនជាតិខ្មែរ ,  UNGEGN :  Chônchéatĕ Khmêr ,  ALA-LC :  Janajāti Khmaer   [cɔn.ciət   kʰmae] ) are an  Austroasiatic   ethnic group  native to  Cambodia . They comprise over 95% of Cambodia's population of 17 million. [ 15 ]  They speak the  Khmer language , which is part of the larger  Austroasiatic language family  alongside  Mon  and  Vietnamese .


The majority of Khmer people follow  Theravada Buddhism . Significant populations of Khmers reside in adjacent areas of  Thailand  ( Northern Khmer ) and the  Mekong Delta  region of neighboring  Vietnam  ( Khmer Krom ), while there are over one million Khmers in the Khmer diaspora living mainly in  France , the  United States , and  Australia .


The majority of the world's Khmers live in Cambodia, the population of which is over 95% Khmer. [ 15 ] [ 16 ] [ 17 ]


There are also significant Khmer populations native to  Thailand  and  Vietnam . In Thailand, there are over one million Khmers (known as the  Khmer Surin ), mainly in  Surin  ( Sorin ),  Buriram  ( Borei Rom ) and  Sisaket  ( Srei Saket ) provinces. Estimates for the number of the Khmers in Vietnam (known as the  Khmer Krom ) vary from the 1.3 million given by government data to 7 million advocated by the  Khmers Kampuchea-Krom Federation . [ 18 ]  The Khmer population native to  Laos  is less significant than in Thailand and Vietnam, those communities reside in the southwestern tip of Laos, at the borders of Thailand and Cambodia. [ 19 ]


Due to migration as a result of the  Cambodian civil war  and  Cambodian genocide , there is a large Khmer diaspora residing in the United States, Canada, Australia, and France.


According to one Khmer legend attributed by  George Coedes  to a tenth century inscription, the Khmers arose from the union of the Brahmana  Kambu Swayambhuva  and the  apsara  ("celestial nymph") Mera. Their marriage is said to have given rise to the name  Khmer  and founded the  Varman dynasty  of ancient Cambodia. [ 32 ]


A more popular legend, reenacted to this day in the traditional Khmer wedding ceremony and taught in elementary school, holds that Cambodia was created when a merchant named  Kaundinya I  (commonly referred to as  Preah Thong ) married Princess  Soma , a  Nāga  ( Neang Neak ) princess. Kaundinya sailed to Southeast Asia following an arrow he saw in a dream. Upon arrival he found an island called  Kok Thlok  and, after conquering Soma's Naga army, he fell in love with her. As a dowry, the father of princess Soma drank the waters around the island, which was revealed to be the top of a mountain, and the land below that was uncovered became Cambodia. Kaundinya and Soma and their descendants became known as the Khmers and are said to have been the rulers of  Funan ,  Chenla  and the  Khmer Empire . [ 33 ]  This myth further explains why the oldest Khmer  wats , or temples, were always built on mountaintops, and why today mountains themselves are still revered as holy places.


The Khmers, an  Austroasiatic people , are one of the oldest ethnic groups in the area, having filtered into Southeast Asia from  southern China , [ 34 ]  possibly  Yunnan , or from  Northeast India  around the same time as the  Mon , who settled further west on the  Indochinese Peninsula  and to whom the Khmer are ancestrally related. [ 35 ]  Most archaeologists and linguists, and other specialists like  Sinologists  and crop experts, believe that they arrived no later than 2000 BCE (over four thousand years ago) bringing with them the practice of agriculture and in particular the cultivation of  rice . This region is also one of the first places in the world to use  bronze . They were the builders of the later  Khmer Empire , which dominated Southeast Asia for six centuries beginning in 802, and now form the mainstream of political, cultural, and economic Cambodia. [ 36 ]


The Khmers developed the  Khmer alphabet , which in turn gave birth to the later  Thai  and  Lao alphabets . The Khmers are considered by  archaeologists  and  ethnologists  to be indigenous to the contiguous regions of  Isan , southern  Laos ,  Cambodia  and  South Vietnam . That is to say the Cambodians have historically been a lowland people who lived close to one of the tributaries of the  Mekong River . The reason they migrated into Southeast Asia is not well understood, but scholars believe that  Austroasiatic  speakers were pushed south by invading  Tibeto-Burman speakers  from the north as evident by Austroasiatic vocabulary in Chinese, because of agricultural purposes as evident by their migration routes along major rivers, or a combination of these and other factors.


The Khmer are considered a part of the  Indian cultural sphere , owing to them adopting Indian culture, traditions and religious identities. The first powerful trading kingdom in Southeast Asia, the  Kingdom of Funan , was established in southeastern Cambodia and the Mekong Delta in the first century, although extensive archaeological work in  Angkor Borei District  near the modern Vietnamese border has unearthed brickworks, canals, cemeteries and graves dating to the fifth century BCE.


During the Funan period (1st–6th centuries CE) the Khmer also acquired Buddhism, the concept of the  Shaiva   imperial cult  of the  devaraja  and the great temple as a symbolic  world mountain . The rival Khmer  Chenla Kingdom  emerged in the fifth century and later conquered the Kingdom of Funan. Chenla was an upland state whose economy was reliant on agriculture whereas Funan was a lowland state with an economy dependent on maritime trade.


These two states, even after conquest by Chenla in the sixth century, were constantly at war with each other and smaller principalities. During the Chenla period (5th–8th centuries), Khmers left the world's earliest known  zero  in one of their temple inscriptions. Only when  King Jayavarman II  declared an independent and united Cambodia in 802 was there relative peace between the two lands, upper and lowland Cambodia.


Jayavarman II  (802–830) revived Khmer power and built the foundation for the Khmer Empire, founding three capitals— Indrapura ,  Hariharalaya , and  Mahendraparvata —the archeological remains of which reveal much about his times. After winning a long civil war,  Suryavarman I  (reigned 1002–1050) turned his forces eastward and subjugated the Mon kingdom of  Dvaravati . Consequently, he ruled over the greater part of present-day Thailand and Laos, as well as the northern half of the Malay Peninsula. This period, during which  Angkor Wat  was constructed, is considered the apex of Khmer civilization.


The Khmer kingdom became the  Khmer Empire  and the great temples of Angkor, considered an archeological treasure replete with detailed stone bas-reliefs showing many aspects of the culture, including some musical instruments, remain as monuments to the culture of the Cambodia. After the death of  Suryavarman II  (1113–1150), Cambodia lapsed into chaos until  Jayavarman VII  (1181–1218) ordered the construction of a new city. He was a Buddhist, and for a time, Buddhism became the dominant religion in Cambodia. As a state religion, however, it was adapted to suit the Deva Raja cult, with a Buddha Raja being substituted for the former Shiva Raja or Vishnu Raja.


The rise of the  Tai  kingdoms of  Sukhothai  (1238) and  Ayutthaya  (1350) resulted in almost ceaseless wars with the Khmers and led to the destruction of Angkor in 1431. They are said to have carried off 90,000 prisoners, many of whom were likely dancers and musicians. [ 37 ]  The period following 1432, with the Khmer people bereft of their treasures, documents, and human culture bearers, was one of precipitous decline.


In 1434, King  Ponhea Yat  made  Phnom Penh  his capital, and Angkor was abandoned to the jungle. Due to continued Siamese and Vietnamese aggression, Cambodia appealed to France for protection in 1863 and became a French protectorate in 1864. During the 1880s, along with southern Vietnam and Laos, Cambodia was drawn into the French-controlled Indochinese Union. For nearly a century, the French exploited Cambodia commercially, and demanded power over politics, economics, and social life.


During the second half of the twentieth century, the political situation in Cambodia became chaotic. King  Norodom Sihanouk  (later, Prince, then again King), proclaimed Cambodia's independence in 1949 (granted in full in 1953) and ruled the country until March 18, 1970, when he was overthrown by General  Lon Nol , who established the Khmer Republic. On April 17, 1975,  Khmer Rouge , who under the leadership of  Pol Pot  combined  Khmer nationalism  and extreme  Communism , came to power and virtually destroyed the Cambodian people, their health, morality, education, physical environment, and culture in the  Cambodian genocide .


On January 7, 1979, Vietnamese forces  ousted the Khmer Rouge . After more than ten years of painfully slow rebuilding, with only meager outside help, the United Nations intervened resulting in the Paris Peace Accord on October 23, 1992, and created conditions for general elections in May 1993, leading to the formation of the current government and the restoration of Prince Sihanouk to power as King in 1993.


The culture of the ethnic Khmers is fairly homogeneous throughout their geographic range. Regional dialects exist, but are mutually intelligible. The standard is based on the dialect spoken throughout the  Central Plain , [ 38 ]  a region encompassed by the northwest and central provinces. The varieties of Khmer spoken in this region are representative of the speech of the majority of the population. A unique and immediately recognizable dialect has developed in Phnom Penh that, due to the city's status as the national capital, has been modestly affected by recent French and Vietnamese influence. Other dialects are  Northern Khmer dialect , called  Khmer Surin  by Khmers, spoken by over a million  Khmer native to Northeast Thailand ; and  Khmer Krom  spoken by the millions of Khmer native to the  Mekong Delta  regions of Vietnam adjacent to Cambodia and their descendants abroad. A little-studied dialect known as  Western Khmer , or Cardamom Khmer, is spoken by a small, isolated population in the  Cardamom Mountain range  extending from Cambodia into eastern Central Thailand. Although little studied, it is unique in that it maintains a definite system of  vocal register  that has all but disappeared in other dialects of modern Khmer.
The modern Khmer strongly identify their ethnic identity with their religious beliefs and practices, which combine the tenets of Theravada Buddhism with elements of indigenous ancestor-spirit worship, animism and shamanism. [ 39 ]  Most Cambodians, whether or not they profess to be Buddhists or other faiths, believe in a rich supernatural world. Several types of supernatural entities are believed to exist; they make themselves known by means of inexplicable sounds or happenings. Among these phenomena are  kmaoch  ខ្មោច (ghosts),  pret  ប្រែត (comes in many forms depending on their punishments) and  beisach  បិសាច(monsters) [these are usually the spirits of people who have died a violently, untimely, or unnatural deaths];  arak  អារក្ស (evil spirits, devils),  ahp   krasue ,  neak ta  អ្នកតា (tutelary spirit or entity residing in inanimate objects; land, water, trees etc.),  chomneang/mneang phteah  ជំនាងផ្ទះ/ម្នាងផ្ទះ(house guardians),  meba  មេបា (ancestral spirits), and  mrenh kongveal  ម្រេញគង្វាល (little mischief spirit guardians dressed in red). [ 40 ]  All spirits must be shown proper respect, and, with the exception of the  mneang phteah  and  mrenh kongveal , they can cause trouble ranging from mischief to serious life-threatening illnesses.


The majority of the Cambodians live in rural villages either as rice farmers or fishermen. Their life revolves around the  Wat  (temple) and the various Buddhist ceremonies throughout the year.
However, if Cambodians become ill, they will frequently see a  kru khmae  (shaman/healer), whom they believe can diagnose which of the many spirits has caused the illness and recommend a course of action to propitiate the offended spirit, thereby curing the illness. [ 41 ]  The  kru khmae  is also learned in herb lore and is often sought to prepare various "medicines" and potions or for a  magical tattoo , all believed to endow one with special prowess and ward off evil spirits or general bad luck. [ 41 ]  Khmer beliefs also rely heavily on  astrology , a remnant of Hinduism. A fortune teller, called  hao-ra  (astrologists) or  kru teay  in Khmer, is often consulted before major events, like choosing a spouse, beginning an important journey or business venture, setting the date for a wedding and determining the proper location for building new structures. Throughout the year, the Cambodian celebrate many holidays, most of a religious or spiritual nature, some of which are also observed as  public holidays . The two most important are  Chol Chhnam  ( Cambodian New Year ) and  Pchum Ben  ("Ancestor Day"). The Cambodian  Buddhist calendar  is divided into 12 months with the traditional new year beginning on the first day of  khae chaet , which coincides with the first  new moon  of April in the western calendar. The modern celebration has been standardized to coincide with April 13. Dance occupies a central place for the Khmer people, one of its earliest records dates back to the 7th century, where performances were used as a funeral rite for kings. [ 42 ]  In the 20th century, the use of dancers is also attested in funerary processions, such as that for King  Sisowath Monivong . During the  Angkor  period, dance was ritually performed at temples. [ 43 ]  The temple dancers came to be considered as apsaras, who served as entertainers and messengers to divinities. [ 44 ]  Ancient stone inscriptions describe thousands of apsara dancers assigned to temples and performing divine rites as well as for the public. [ 43 ]  The Khmer classical dance was placed in 2003 on the UNESCO World Heritage List.


Cambodian culture  has influenced  Thai  and  Lao  cultures and vice versa. Many Khmer loanwords are found in  Thai  and  Lao , while many Lao and Thai loanwords are found in Khmer. The  Thai  and  Lao  alphabets are also derived from the  Khmer script . [ 45 ]


The Khmer people are genetically closely related to other Southeast Asian populations. They show strong genetic relation to other  Austroasiatic  people in  Southeast Asia  and  East Asia  and have a minor genetic influence from  Indian people . [ 46 ]  Cambodians trace about 16% of their ancestry to a  Eurasian  population that is equally related to both  Europeans  and  East Asians , while the remaining 84% of their ancestry is related to other Southeast Asians, particularly to a source similar to the  Dai people . [ 47 ]  Another study suggests that Cambodians trace about 19% of their ancestry to a similar Eurasian population related to modern-day  Central Asians ,  South Asians , and  East Asians , while the remaining 81% of their ancestry is related specifically to modern-day Dai and  Han people . [ 48 ]


The  genetic testing  website  23andMe  groups Khmer people under the "Indonesian, Khmer, Thai & Myanmar" reference population. This reference population contains people who have had recent ancestors from Cambodia, Indonesia, Laos, Malaysia, Myanmar and Thailand. [ 49 ]


Hideo Matsumoto, professor  emeritus  at  Osaka Medical College  tested Gm types, genetic markers of  immunoglobulin G , of Khmer people for a 2009 study. [ 50 ]  The study found that the Gm afb1b3 is a southern marker gene possibly originating in  southern China  and found at high frequencies across southern China,  Southeast Asia ,  Taiwan ,  Sri Lanka ,  Bangladesh ,  Nepal ,  Assam  and parts of the  Pacific Islands . [ 50 ]  The study found that the average frequency of Gm afb1b3 was 76.7% for the Khmer population. [ 50 ]


Magnetogenetics  is a medical research technique whereby  magnetic fields  are used to affect cell function. [ 1 ]


The development of genetic technologies that can modulate cellular processes has greatly contributed to biological research. A representative example is the development of  optogenetics , which is a neuromodulation tool kit that involves light-sensitive proteins such as opsins. This progress provided the grounds for a breakthrough in linking the causal relationship between neuronal activity and behavioral outcome.


The foremost strength of the genetic toolkits used in neuromodulation is that it can provide either spatially or temporally, or both, precise modulation of the brain nervous system. To date, several technologies are adapted with genetics (e.g.  optogenetics ,  chemogenetics , etc.), and each technology has strengths and limits. For example,  optogenetics  has advantages in that it can provide temporally and spatially precise manipulation of neurons. On the other hand, it involves light stimulation, which cannot penetrate tissues effectively and requires implanted optical devices, limiting its applications for  in vivo  live animal studies


Techniques that rely on the magnetic control of cellular process are relatively new. This technique may provide an approach that does not require implantation of invasive electrodes or optical devices. This method will allow penetration in to the deeper region of the brain, and may have lower response latency. [ 2 ]  In 1980, Young and colleagues have shown that magnetic fields with magnitudes in millitesla range are able to penetrate into the brain without attenuation of the signal or side effects because of the negligible magnetic susceptibility and low conductivity of biological tissue. [ 3 ]  Early attempts to manipulate electrical signaling within brain using magnetic fields was performed by Baker et al., who later developed devices for  transcranial magnetic stimulation  (TMS) in 1985.


To apply magnetogenetics in biological and neuroscientific research, fusing  TRPV  class receptors with a paramagnetic protein (typically  ferritin ) was suggested. These paramagnetic proteins, which typically contain iron or have iron-containing cofactors, are then magnetically stimulated. How this technique can modulate neuronal activity remains unclear but it is thought that the ion channels are activated and opened either by mechanical force exerted by the paramagnetic proteins, or by heating of these via magnetic stimulation. However, availability of such paramagnetic proteins as a transducer for magnetic field to mechanical or temperature stimuli is controversial.


On the other hand, nanoparticles have been suggested as possible candidates that can function as the transducer of magnetic field to the stimulus cue. Based on this concept, next generation of magnetogenetics technique is being developed. In 2010, Arnd Pralle and colleges showed that the first in vivo magneto-thermal stimulation of heat sensitive ion channel  TRPV1  that employs magnetic nanoparticles as a transducer in  C. elegans . [ 4 ]  In 2012, Seung Chan Kim showed gene expression profile change of total human genome approximately 30,000 genes using 0.2T static magnetic fields. [ 5 ]  In 2015,  Polina Anikeeva 's research group demonstrated that similar concept can enhance the neuronal signals in mammalian brain. [ 6 ]  In 2021,  Jinwoo Cheon 's research group has successfully developed the magneto-mechanical genetics which uses magnetic stimulation derived mechanical force in mammalian. [ 7 ]  In this study, magnetic torque by rotating magnetic field was employed to activate the mechanosensitive cation channel  Piezo1 . Results of this study show that remote,  in vivo  manipulation of behavior of mice can be done using magnetogenetics. Cheon's group further developed a magnetogenetic system enables cell-type-specific modulation of deep brain neural circuits. [ 8 ]  This was achieved by combining Piezo1 ion channels and Cre-loxP technology, allowing precise, reversible, and wireless control of neuronal activity in freely moving animals. The study demonstrated significant potential for neuroscience research by demonstrating several applications such as feeding behavior modulation, long-term obesity control, and social interaction studies. This torque-based system developed by Cheon is anticipated to be valuable not only for neuroscience research but also for various deep tissue in vivo applications and therapeutics.


One of the main issues in magnetogenetics is related the physical properties of the  ferritin . [ 9 ]  The ferritin is composed of 24 subunits of protein complex and a small iron oxide core. The core of the ferritin is in the form of  ferric hydroxide  which has  antiferromagnetic  properties. Some researchers have reported that ferritin has remnant magnetization due to their intrinsic defect and impurities. [ 10 ]  However, even with optimistic calculations, the magnetic interaction energy for heat or force generation is several orders below than  thermal fluctuation energy . Recently, other researchers hypothesized that there are other possible mechanisms for activate the ion channels, but these studies remain inconclusive.


Marker assisted selection  or  marker aided selection  ( MAS ) is an indirect selection process where a  trait  of interest is selected based on a  marker  ( morphological ,  biochemical  or  DNA / RNA  variation) linked to a trait of interest (e.g. productivity, disease resistance, abiotic stress tolerance, and quality), rather than on the trait itself. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ]  This process has been extensively researched and proposed for  plant-  and  animal - breeding. [ 5 ]


For example, using MAS to select individuals with disease resistance involves identifying a marker  allele  that is linked with disease resistance rather than the level of disease resistance. The assumption is that the marker associates at high frequency with the  gene  or  quantitative trait locus  (QTL) of interest, due to genetic linkage (close proximity, on the chromosome, of the marker locus and the disease resistance-determining locus). MAS can be useful to select for traits that are difficult or expensive to measure, exhibit low  heritability  and/or are expressed late in development. At certain points in the breeding process the specimens are examined to ensure that they express the desired trait.


The majority of MAS work in the present era uses DNA-based markers. [ 5 ]  However, the first markers that allowed indirect selection of a trait of interest were morphological markers.  In 1923, Karl Sax first reported association of a simply inherited  genetic marker  with a quantitative trait in plants when he observed segregation of seed size associated with segregation for a seed coat color marker in beans ( Phaseolus vulgaris  L.). [ 6 ]   In 1935, J. Rasmusson demonstrated linkage of flowering time (a quantitative trait) in  peas  with a simply inherited gene for flower color. [ 7 ]


Markers may be:


The following terms are generally less relevant to discussions of MAS in plant and animal breeding, but are highly relevant in molecular biology research:


A distinction can be made between selectable markers (which eliminate certain genotypes from the population) and screenable markers (which cause certain genotypes to be readily identifiable, at which point the experimenter must "score" or evaluate the population and act to retain the preferred genotypes).  Most MAS uses screenable markers rather than selectable markers.


The gene of interest directly causes production of protein(s) or RNA that produce a desired trait  or phenotype, whereas markers (a DNA sequence or the morphological or biochemical markers produced due to that DNA) are genetically linked to the gene of interest.  The gene of interest and the marker tend to move together during segregation of gametes due to their proximity on the same chromosome and concomitant reduction in  recombination  (chromosome crossover events) between the marker and gene of interest. For some traits, the gene of interest has been discovered and the presence of desirable alleles can be directly assayed with a high level of confidence. However, if the gene of interest is not known, markers linked to the gene of interest can still be used to select for individuals with desirable alleles of the gene of interest.  When markers are used there may be some inaccurate results due to inaccurate tests for the marker.   There also can be false positive results when markers are used, due to recombination between the marker of interest and gene (or QTL). A perfect marker would elicit no false positive results.  The term 'perfect marker' is sometimes used when tests are performed to detect a SNP or other DNA polymorphism in the gene of interest, if that SNP or other polymorphism is the direct cause of the trait of interest.   The term 'marker' is still appropriate to use when directly assaying the gene of interest, because the test of genotype is an indirect test of the trait or phenotype of interest. [ citation needed ]


An ideal marker:


Morphological markers are associated with several general deficits that reduce their usefulness including:


To avoid problems specific to morphological markers, DNA-based markers have been developed. They are highly  polymorphic , exhibit simple inheritance (often codominant), are abundant throughout the genome, are easy and fast to detect, exhibit minimum pleiotropic effects, and detection is not dependent on the developmental stage of the organism. Numerous markers have been mapped to different chromosomes in several crops including rice, wheat, maize, soybean and several others, and in livestock such as cattle, pigs and chickens. Those markers have been used in diversity analysis, parentage detection, DNA fingerprinting, and prediction of hybrid performance. Molecular markers are useful in indirect selection processes, enabling manual selection of individuals for further propagation.


'Major genes' that are responsible for economically important characteristics are frequent in the plant kingdom. Such characteristics include disease resistance, male sterility, [ 12 ]  self-incompatibility, and others related to shape, color, and architecture of whole plants and are often of mono- or oligogenic in nature. The marker loci that are tightly linked to major genes can be used for selection and are sometimes more efficient than direct selection for the target gene. Such  advantages in efficiency may be due for example, to higher expression of the marker mRNA in such cases that the marker is itself a gene. Alternatively, in such cases that the target gene of interest differs between two alleles by a difficult-to-detect  single nucleotide polymorphism , an external marker (be it another gene or a polymorphism that is easier to detect, such as a  short tandem repeat ) may present as the most realistic option.


There are several indications for the use of molecular markers in the selection of a genetic trait.


Situations such as:


The cost of  genotyping  (for example, the molecular marker assays needed here) is decreasing thus increasing the attractiveness of MAS as the development of the technology continues. (Additionally, the cost of  phenotyping  performed by a human is a  labor burden , which is higher in a developed country and increasing in a developing country.)


Generally the first step is to  map  the gene or  quantitative trait locus  (QTL) of interest first by using different techniques and then using this information for marker assisted selection. Generally, the markers to be used should be close to gene of interest (<5  recombination unit  or cM) in order to ensure that only minor fraction of the selected individuals will be recombinants. Generally, not only a single marker but rather two markers are used in order to reduce the chances of an error due to homologous recombination. For example, if two flanking markers are used at same time with an interval between them of approximately 20cM, there is higher probability (99%) for recovery of the target gene.


In plants QTL mapping is generally achieved using bi-parental cross populations; a cross between two parents which have a contrasting phenotype for the trait of interest are developed. Commonly used populations are near isogenic lines (NILs), recombinant inbred lines (RILs),  doubled haploids  (DH), back cross and F 2 . Linkage between the phenotype and markers which have already been mapped is tested in these populations in order to determine the position of the QTL. Such techniques are based on linkage and are therefore referred to as " linkage mapping ".A


In contrast to two-step QTL mapping and MAS, a single-step method for breeding typical plant populations has been developed. [ 13 ] [ 14 ]


In such an approach, in the first few breeding cycles, markers linked to the trait of interest are identified by QTL mapping and later the same information is used in the same population. In this approach, pedigree structure is created from families that are created by crossing number of parents (in three-way or four way crosses). Both phenotyping and genotyping is done using molecular markers mapped the possible location of QTL of interest. This will identify markers and their favorable alleles. Once these favorable marker alleles are identified, the frequency of such alleles will be increased and response to marker assisted selection is estimated. Marker allele(s) with desirable effect will be further used in next selection cycle or other experiments.


Recently high-throughput genotyping techniques are developed which allows marker aided screening of many genotypes. This will help breeders in shifting traditional breeding to marker aided selection. One example of such automation is using DNA isolation robots, capillary electrophoresis and pipetting robots.


One recent example of capllilary system is Applied Biosystems 3130 Genetic Analyzer. This is the latest generation of 4-capillary electrophoresis instruments for the low to medium throughput laboratories.


High-throughput MAS is needed for  crop breeding  because current techniques are not cost effective. Arrays have been developed for rice by Masouleh et al 2009; wheat by Berard et al 2009, Bernardo et al 2015, and Rasheed et al 2016; legumes by Varshney et al 2016; and various other crops, but all of these have also problems with customization, cost, flexibility, and equipment costs. [ 15 ]


A minimum of five or six- backcross  generations are required to transfer a gene of interest from a donor (may not be adapted) to a recipient (recurrent – adapted cultivar). The recovery of the recurrent genotype can be accelerated with the use of molecular markers. If the  F1  is heterozygous for the marker  locus , individuals with the recurrent parent  allele(s)  at the marker locus in first or subsequent backcross generations will also carry a chromosome tagged by the marker.


Gene pyramiding  has been proposed and applied to enhance resistance to disease and insects by selecting for two or more than two genes at a time. For example, in rice such pyramids have been developed against bacterial blight and blast. The advantage of use of markers in this case allows to select for QTL-allele-linked markers that have same phenotypic effect.


MAS has also been proved useful for  livestock  improvement. [ 16 ]


A coordinated effort to implement wheat ( Durum  ( Triticum turgidum ) and common wheat ( Triticum aestivum )) marker assisted selection in the U.S. as well as a resource for marker assisted selection exists at the Wheat CAP ( Coordinated Agricultural Project ) website.


MASS syndrome  is a  medical disorder  of the connective tissue similar to  Marfan syndrome .
MASS stands for  m itral valve prolapse ,  a ortic root  diameter at upper limits of normal for body size,  s tretch marks  of the skin, and  s keletal conditions  similar to Marfan syndrome. It is caused by a mutation in the  FBN1  gene, which encodes  fibrillin-1 . [ 2 ]  Fibrillin-1 is an extracellular matrix protein that is found in  microfibrils ; [ 3 ]  defects in the fibrillin-1 protein cause the malfunctioning of microfibrils, [ 4 ]  which results in improper stretching [ 4 ]  of ligaments, blood vessels, and skin.


Treatment options for MASS syndrome are largely determined on a case-by-case basis and generally address the symptoms as opposed to the cause of the disorder. [ 5 ]  Due to the similarities between MASS syndrome and Marfan syndrome, the treatment plans are also similar. [ 6 ]


Other possible symptoms are  mitral valve prolapse , a large aortic root diameter, and  myopia . [ 2 ]  The skeletal features found in MASS syndrome include curvature of the spine ( scoliosis ), chest wall deformities, and joint  hypermobility . [ 2 ]


MASS syndrome and Marfan syndrome are overlapping  connective tissue disorders . Both can be caused by mutations in the gene encoding a protein called fibrillin. These conditions share many of the same signs and symptoms including long limbs and fingers, chest wall abnormalities (indented chest bone or protruding chest bone), flat feet, scoliosis, mitral valve prolapse, loose or hypextensible joints, highly arched roof of the mouth, and mild dilatation of the aortic root. Unlike in Marfan syndrome,  aneurysm  does not develop. [ 2 ]


Individuals with MASS syndrome do not have progressive aortic enlargement or  lens dislocation , while people with Marfan syndrome do. Skin involvement in MASS syndrome is typically limited to stretch marks ( striae distensae ). Also, the skeletal manifestations of MASS syndrome are generally mild. [ citation needed ]


A  maternal effect  is a situation where the  phenotype  of an organism is determined not only by the environment it experiences and its  genotype , but also by the environment and genotype of its mother. In  genetics , maternal effects occur when an organism shows the phenotype expected from the genotype of the mother, irrespective of its own genotype, often due to the mother supplying  messenger RNA  or  proteins  to the egg. Maternal effects can also be caused by the maternal environment independent of genotype, sometimes controlling the  size, sex, or behaviour of the offspring . These adaptive maternal effects lead to phenotypes of offspring that increase their fitness. Further, it introduces the concept of  phenotypic plasticity , an important evolutionary concept. It has been proposed that maternal effects are important for the evolution of adaptive responses to  environmental heterogeneity .


In  genetics , a maternal effect occurs when the phenotype of an organism is determined by the genotype of its mother. [ 1 ]  For example, if a mutation is maternal effect  recessive , then a female homozygous for the mutation may appear phenotypically normal, however her offspring will show the mutant phenotype, even if they are heterozygous for the mutation.


Maternal effects often occur because the mother supplies a particular  mRNA  or  protein  to the oocyte, hence the maternal genome determines whether the molecule is functional. Maternal supply of mRNAs to the early embryo is important, as in many organisms the embryo is initially transcriptionally inactive. [ 2 ]  Because of the inheritance pattern of maternal effect mutations, special  genetic screens  are required to identify them. These typically involve examining the phenotype of the organisms one generation later than in a conventional ( zygotic ) screen, as their mothers will be potentially homozygous for maternal effect mutations that arise. [ 3 ] [ 4 ]


A  Drosophila melanogaster   oocyte  develops in an egg chamber in close association with a set of cells called  nurse cells . Both the oocyte and the nurse cells are descended from a single germline  stem cell , however  cytokinesis  is incomplete in these  cell divisions , and the cytoplasm of the nurse cells and the oocyte is connected by structures known as  ring canals . [ 5 ]  Only the oocyte undergoes  meiosis  and contributes  DNA  to the next generation.


Many maternal effect  Drosophila  mutants have been found that affect the early steps in embryogenesis such as  axis determination , including  bicoid ,  dorsal ,  gurken  and  oskar . [ 6 ] [ 7 ] [ 8 ]  For example, embryos from homozygous  bicoid  mothers fail to produce head and  thorax  structures.


Once the gene that is disrupted in the  bicoid  mutant was identified, it was shown that  bicoid  mRNA is  transcribed  in the nurse cells and then relocalized to the oocyte. [ 9 ]  Other maternal effect mutants either affect products that are similarly produced in the nurse cells and act in the oocyte, or parts of the transportation machinery that are required for this relocalization. [ 10 ]  Since these genes are expressed in the (maternal) nurse cells and not in the oocyte or fertilised embryo, the maternal genotype determines whether they can function.


Maternal effect genes [ 11 ]  are expressed during oogenesis by the mother (expressed prior to fertilization) and develop the anterior-posterior and dorsal ventral polarity of the egg. The anterior end of the egg becomes the head; posterior end becomes the tail. the dorsal side is on the top; the ventral side is in underneath. The products of maternal effect genes called maternal mRNAs are produced by nurse cell and follicle cells and deposited in the egg cells (oocytes). At the start of development process, mRNA gradients are formed in oocytes along anterior-posterior and dorsal ventral axes.


About thirty maternal genes are involved in pattern formation have been identified. In particular, products of four maternal effect genes are critical to the formation of anterior-posterior axis. The product of two maternal effect gene, bicoid and hunchback, regulates formation of anterior structure while another pair nanos and caudal, specifies protein that regulates formation of posterior part of embryo.


The transcript of all four genes-bicoid, hunchback, caudal, nanos are synthesized by nurse and follicle cells and transported into the oocytes.


In birds, mothers may pass down hormones in their eggs that affect an offspring's growth and behavior. Experiments in  domestic canaries  have shown that eggs that contain more yolk androgens develop into chicks that display more social dominance. Similar variation in yolk androgen levels has been seen in bird species like the  American coot , though the mechanism of effect has yet to be established. [ 12 ]


In 2015, obesity theorist Edward Archer published "The Childhood Obesity Epidemic as a Result of Nongenetic Evolution: The Maternal Resources Hypothesis" and a series of works on maternal effects in human  obesity  and health. [ 13 ] [ 14 ] [ 15 ] [ 16 ]  In this body of work, Archer argued that accumulative maternal effects via the non-genetic evolution of matrilineal nutrient metabolism is responsible for the increased global prevalence of obesity and  diabetes mellitus type 2 . Archer posited that decrements in maternal metabolic control altered fetal pancreatic  beta cell ,  adipocyte  (fat cell) and  myocyte  (muscle cell) development thereby inducing an enduring competitive advantage of adipocytes in the acquisition and sequestering on nutrient energy.


The environmental cues such as light, temperature, soil moisture and nutrients that the mother plant encounters can cause variations in seed quality, even within the same genotype. Thus, the mother plant greatly influences seed traits such as seed size, germination rate, and viability. [ 17 ]


The environment or condition of the mother can also in some situations influence the phenotype of her offspring, independent of the offspring's genotype.


In contrast, a  paternal effect  is when a phenotype results from the genotype of the father, rather than the genotype of the individual. [ 18 ]  The genes responsible for these effects are components of  sperm  that are involved in  fertilization  and early development. [ 19 ]  An example of a paternal-effect gene is the ms(3)sneaky in  Drosophila . Males with a mutant  allele  of this gene produce sperm that are able to fertilize an egg, but the sneaky-inseminated eggs do not develop normally. However, females with this mutation produce eggs that undergo normal development when fertilized. [ 20 ]


Adaptive maternal effects induce phenotypic changes in offspring that result in an increase in fitness. [ 21 ]  These changes arise from mothers sensing environmental cues that work to reduce offspring fitness, and then responding to them in a way that then “prepares” offspring for their future environments. A key characteristic of “adaptive maternal effects” phenotypes is their plasticity. Phenotypic plasticity gives organisms the ability to respond to different environments by altering their phenotype. With these “altered” phenotypes increasing fitness it becomes important to look at the likelihood that adaptive maternal effects will evolve and become a significant phenotypic adaptation to an environment.


When traits are influenced by either the maternal environment or the maternal phenotype, it is said to be influenced by maternal effects.  Maternal effects work to alter the phenotypes of the offspring through pathways other than DNA. [ 22 ]   Adaptive  maternal effects are when these maternal influences lead to a phenotypic change that increases the fitness of the offspring. [ 23 ]  In general, adaptive maternal effects are a mechanism to cope with factors that work to reduce offspring fitness; [ 24 ]  they are also environment specific.


It can sometimes be difficult to differentiate between maternal and adaptive maternal effects. Consider the following: Gypsy moths reared on foliage of black oak, rather than chestnut oak, had offspring that developed faster. [ 25 ]  This is a maternal,  not  an adaptive maternal effect. In order to be an adaptive maternal effect, the mother's environment would have to have led to a change in the eating habits or behavior of the offspring. [ 25 ]  The key difference between the two therefore, is that adaptive maternal effects are environment specific. The phenotypes that arise are in response to the mother sensing an environment that would reduce the fitness of her offspring. By accounting for this environment she is then able to alter the phenotypes to actually increase the offspring's fitness.  Maternal  effects are not in response to an environmental cue, and further they have the potential to increase offspring fitness, but they may not.


When looking at the likelihood of these “altered” phenotypes evolving there are many factors and cues involved. Adaptive maternal effects evolve only when offspring can face many potential environments; when a mother can “predict” the environment into which her offspring will be born; and when a mother can influence her offspring's phenotype, thereby increasing their fitness. [ 25 ]  The summation of all of these factors can then lead to these “altered” traits becoming favorable for evolution.


The phenotypic changes that arise from adaptive maternal effects are a result of the mother sensing that a certain aspect of the environment may decrease the survival of her offspring. When sensing a cue the mother “relays” information to the developing offspring and therefore induces adaptive maternal effects. This tends to then cause the offspring to have a higher fitness because they are “prepared” for the environment they are likely to experience. [ 24 ]  These cues can include responses to predators, habitat, high population density, and food availability [ 26 ] [ 27 ] [ 28 ]


The increase in size of Northern American red squirrels is a great example of an adaptive maternal effect producing a phenotype that resulted in an increased fitness. The adaptive maternal effect was induced by the mothers sensing the high population density and correlating it to low food availability per individual. Her offspring were on average larger than other squirrels of the same species; they also grew faster. Ultimately, the squirrels born during this period of high population density showed an increased survival rate (and therefore fitness) during their first winter. [ 26 ]


When analyzing the types of changes that can occur to a phenotype, we can see changes that are behavioral, morphological, or physiological. A characteristic of the phenotype that arises through adaptive maternal effects, is the plasticity of this phenotype.  Phenotypic plasticity  allows organisms to adjust their phenotype to various environments, thereby enhancing their fitness to changing environmental conditions. [ 24 ]  Ultimately it is a key attribute to an organism's, and a population's, ability to adapt to short term environmental change. [ 29 ] [ 30 ]


Phenotypic plasticity can be seen in many organisms, one species that exemplifies this concept is the seed beetle  Stator limbatus . This seed beetle reproduces on different host plants, two of the more common ones being  Cercidium floridum  and  Acacia greggii . When  C. floridum  is the host plant, there is selection for a large egg size; when  A. greggii  is the host plant, there is a selection for a smaller egg size. In an experiment it was seen that when a beetle who usually laid eggs on  A. greggii  was put onto  C. floridum , the survivorship of the laid eggs was lower compared to those eggs produced by a beetle that was conditioned and remained on the  C. florium  host plant. Ultimately these experiments showed the plasticity of egg size production in the beetle, as well as the influence of the maternal environment on the survivorship of the offspring. [ 27 ]


In many insects:


Related to adaptive maternal effects are epigenetic effects.  Epigenetics  is the study of long lasting changes in  gene expression  that are produced by modifications to chromatin instead of changes in DNA sequence, as is seen in DNA mutation.  This "change" refers to  DNA methylation ,  histone acetylation , or the interaction of  non-coding RNAs  with DNA.  DNA methylation is the addition of methyl groups to the DNA. When DNA is methylated in mammals, the transcription of the gene at that location is turned down or turned off entirely. The induction of DNA methylation is highly influenced by the maternal environment. Some maternal environments can lead to a higher methylation of an offspring's DNA, while others lower methylation.[22] [ citation needed ]  The fact that methylation can be influenced by the maternal environment, makes it similar to adaptive maternal effects.  Further similarities are seen by the fact that methylation can often increase the fitness of the offspring. Additionally, epigenetics can refer to histone modifications or non-coding RNAs that create a sort of  cellular memory .  Cellular memory refers to a cell's ability to pass nongenetic information to its daughter cell during replication. For example, after differentiation, a liver cell performs different functions than a brain cell; cellular memory allows these cells to "remember" what functions they are supposed to perform after replication.  Some of these epigenetic changes can be passed down to future generations, while others are reversible within a particular individual's lifetime. This can explain why individuals with identical DNA can differ in their susceptibility to certain chronic diseases.


Currently, researchers are examining the correlations between maternal diet during pregnancy and its effect on the offspring's susceptibility for chronic diseases later in life. The  fetal programming hypothesis  highlights the idea that environmental stimuli during critical periods of fetal development can have lifelong effects on body structure and health and in a sense they prepare offspring for the environment they will be born into. Many of these variations are thought to be due to epigenetic mechanisms brought on by maternal environment such as stress, diet, gestational  diabetes , and exposure to tobacco and alcohol. These factors are thought to be contributing factors to obesity and cardiovascular disease, neural tube defects, cancer, diabetes, etc. [ 32 ]  Studies to determine these epigenetic mechanisms are usually performed through laboratory studies of rodents and epidemiological studies of humans.


Knowledge of maternal diet induced epigenetic changes is important not only for scientists, but for the general public. Perhaps the most obvious place of importance for maternal dietary effects is within the medical field. In the United States and worldwide, many non-communicable diseases, such as cancer, obesity, and heart disease, have reached epidemic proportions. The medical field is working on methods to detect these diseases, some of which have been discovered to be heavily driven by epigenetic alterations due to maternal dietary effects. Once the genomic markers for these diseases are identified, research can begin to be implemented to identify the early onset of these diseases and possibly reverse the epigenetic effects of maternal diet in later life stages. The reversal of epigenetic effects will utilize the pharmaceutical field in an attempt to create drugs which target the specific genes and genomic alterations. The creation of drugs to cure these non-communicable diseases could be used to treat individuals who already have these illnesses. General knowledge of the mechanisms behind maternal dietary epigenetic effects is also beneficial in terms of awareness. The general public can be aware of the risks of certain dietary behaviors during pregnancy in an attempt to curb the negative consequences which may arise in offspring later in their lives. Epigenetic knowledge can lead to an overall healthier lifestyle for the billions of people worldwide.


The effect of maternal diet in species other than humans is also relevant. Many of the long term effects of global climate change are unknown. Knowledge of epigenetic mechanisms can help scientists better predict the impacts of changing community structures on species which are ecologically, economically, and/or culturally important around the world. Since many ecosystems will see changes in species structures, the nutrient availability will also be altered, ultimately affecting the available food choices for reproducing females. Maternal dietary effects may also be used to improve agricultural and aquaculture practices. Breeders may be able to utilize scientific data to create more sustainable practices, saving money for themselves, as well as the consumers.


Hyperglycemia  during pregnancy is thought to cause epigenetic changes in the leptin gene of newborns leading to a potential increased risk for obesity and heart disease.  Leptin  is sometimes known as the “satiety hormone” because it is released by fat cells to inhibit hunger. By studying both animal models and human observational studies, it has been suggested that a leptin surge in the perinatal period plays a critical role in contributing to long-term risk of obesity. The perinatal period begins at 22 weeks gestation and ends a week after birth.[34]  DNA methylation near the leptin locus has been examined to determine if there was a correlation between maternal glycemia and neonatal leptin levels. Results showed that glycemia was inversely associated with the methylation states of LEP gene, which controls the production of the leptin hormone.  Therefore, higher glycemic levels in mothers corresponded to lower methylation states in LEP gene in their children. With this lower methylation state, the LEP gene is transcribed more often, thereby inducing higher blood leptin levels. [ 33 ]   These higher blood leptin levels during the perinatal period were linked to obesity in adulthood, perhaps due to the fact that a higher “normal” level of leptin was set during gestation.  Because obesity is a large contributor to heart disease, this leptin surge is not only correlated with obesity but also heart disease.


High fat diets in utero are believed to cause metabolic syndrome.  Metabolic syndrome  is a set of symptoms including obesity and insulin resistance that appear to be related.  This syndrome is often associated with type II diabetes as well as hypertension and atherosclerosis.  Using mice models, researchers have shown that high fat diets in utero cause modifications to the  adiponectin  and leptin genes that alter gene expression; these changes contribute to metabolic syndrome.  The adiponectin genes regulate glucose metabolism as well as fatty acid breakdown; however, the exact mechanisms are not entirely understood.  In both human and mice models, adiponectin has been shown to add insulin-sensitizing and anti-inflammatory properties to different types of tissue, specifically muscle and liver tissue.  Adiponectin has also been shown to increase the rate of fatty acid transport and oxidation in mice, which causes an increase in fatty acid metabolism. [ 34 ]   With a high fat diet during gestation, there was an increase in methylation in the promoter of the adiponectin gene accompanied by a decrease in acetylation. These changes likely inhibit the transcription of the adiponectin genes because increases in methylation and decreases in acetylation usually repress transcription.  Additionally, there was an increase in methylation of the leptin promoter, which turns down the production of the leptin gene.  Therefore, there was less adiponectin to help cells take up glucose and break down fat, as well as less leptin to cause a feeling of satiety.  The decrease in these hormones caused fat mass gain, glucose intolerance, hypertriglyceridemia, abnormal adiponectin and leptin levels, and hypertension throughout the animal's lifetime.  However, the effect was abolished after three subsequent generations with normal diets. This study highlights the fact that these epigenetic marks can be altered in as many as one generation and can even be completely eliminated over time. [ 35 ]   This study highlighted the connection between high fat diets to the adiponectin and leptin in mice.  In contrast, few studies have been done in humans to show the specific effects of high fat diets in utero on humans.  However, it has been shown that decreased adiponectin levels are associated with obesity, insulin resistance, type II diabetes, and coronary artery disease in humans.  It is postulated that a similar mechanism as the one described in mice may also contribute to metabolic syndrome in humans. [ 34 ]