When can small changes in a DNA sequence have profound effects on a phenotype?
958152
A single nucleotide change in a DNA sequence can result in a change in the codon that could then lead to a change in the amino acid that is made in the protein.  When proteins have a mutation in their amino acid sequence due to the change in DNA sequence, you can get a protein that no longer functions.  This often leads to a disease, and that is a profound effect on a phenotype.  If a DNA change occurs in the promoter of a gene, it's possible that gene which is normally transcribed won't be any more because the transcription factor does not bind recognize the new sequence.  You can also get frame shifts, which would result in a nonsense amino acid sequence.
659200
I'm not sure what you are asking because of the typos. But here goes an answer for what I think you are trying to ask.\n\nA point mutation involving the addition of a BASE early in the coding, The protein resulting from The gene will be entirely different from the point of addition, since the reading frame will be moved forward. \n\nExample (HYPOTHETICAL)\n\nNormal DNA\nATCGGTACCATT\n\nNormal mRNA\nUAGCCAUGGUAA  The reading frame would be UAG-CCA-UGG-UAA...\n\nmutated mRNA (a C added by mistake)\nUAGCCCAUGGUAA The reading frame would be UAG-CCC-AUG-GUA..\n\nThis can cause the protein to be shorter, because it can create a stop codon somewhere with the addition, also it can make it longer, a stop codon no longer present where it should be.\n\nBasically the protein would be non-functioning.
612256
Those portions of DNA are probably difficult to replicate properly (or perfectly I should say).  What's the difference between 5,000 repeats and 4,995?  Not much as far as the cell is concerned.
48539
various mutations, such as a frameshift mutation (shifting of nucleotides), somatic mutation ( lethal), germ cell mutations, inversions, nondisjuctions. Basically just the body making mistakes.
905240
Alterations to DNA are called mutations, and they can result in the formation of new characteristics that are heritable, or capable of being inherited.\n\nEvery cell in the body of every living organism contains DNA in threadlike structures called chromosomes. Stretches of DNA that hold coded instructions for the manufacture of specific proteins are known as genes, of which the human race has approximately 40,000 varieties. If the DNA of a particular gene is altered, that gene may become defective, and the protein for which it codes also may be missing or defective. Just one missing or abnormal protein can have an enormous effect on the entire body: albinism, for instance, is the result of one missing protein.\n\nMutations also can be errors in all or part of a chromosome. Humans normally have 23 pairs of chromosomes, and an extra chromosome can have a tremendous negative impact. For example, there should be two of chromosome 21, as with all other chromosomes, but if there are three, the result is Down syndrome. People with Down syndrome have a unique physical appearance and are developmentally disabled. Nor is an extra chromosome the only chromosomal abnormality that causes problems: if chromosomes 9 and 22 exchange materials, a phenomenon known as translocation, the result can be a certain type of leukemia. Down syndrome also results from translocation.\n\nGerminal mutations are those that occur in the egg or sperm cells and therefore can be passed on to the organism's offspring. Somatic mutations are those that happen in cells other than the sex cells, and they cannot be transmitted to the next generation. This is an important distinction to keep in mind in terms of both the causes and the effects of mutation. If only the somatic cells of the organism are affected, the mutation will not appear in the next generation; on the other hand, if a germinal mutation is involved, what was once an abnormality may become so common in certain populations that it emerges as the norm.\nEvery single human trait—blue eyes, red hair, cystic fibrosis, a second toe longer than the big toe, and so on—is the result of some genetic mutation somewhere back down the line. Traits that are shared by all people must have arisen long ago, while other traits occur only in certain populations of people. Traits may be as innocuous as eye color or hair texture or as grave as a shared tendency toward a particular disease. Cystic fibrosis, for instance, is most common in people of northern European descent, while sickle cell anemia (see Amino Acids) occurs frequently in those of African and Mediterranean ancestry. A fatal disorder known as Tay-Sachs is found primarily in Jewish people whose ancestors came from Eastern Europe. In many cases, the particular mutation, while harmful in one regard, proved to be a useful one for that population. We know, for example, that while two copies of the mutant sickle cell anemia gene cause illness, one copy confers resistance to malaria—a very useful trait to people living in the tropics, where malaria is common.\n\nThe Pima "fat-Storage Mutation."\n\nResearchers have noted a high incidence of obesity among the Pima, a Native American tribe whose ancestral homeland is along the Gila and Salt rivers in Arizona. The Pima tend to eat a diet that is no more fatty than that of the average American—which, of course, means that it is plenty fatty, complete with chips, bologna, ice cream, and all the other high-calorie, low-nutrient foods that most Americans consume. But whereas the average American is over-weight, the average Pima is more dramatically so. This suggests that long ago, when the ancestors of the Pima had to face repeated periods of famine in the dry lands of the American Southwest, survival favored the individual or individuals who had a mutation for fat storage. It so happens that today, there is more than enough food at the local supermarket, but by now the Pima as a group has the fat-stora
512125
in biology, mutations are changes to the genetic material. mutations can be caused by copying errors in the genetic material during cell division and by exposure to radiation, chemicals, or viruses, or can occur deliberately under cellular control during processes such as meiosis or hypermutation. mutations can be classified based on the effect on the structure of the genetic material:\n\n1. small scale mutations affecting one or a few nucleotides\na. point mutation: exchange of a single nucleotide for another through translations or transversions\na)i. silent mutations: code for the same amino acid\na)ii. missense mutations: code for a different amino acid; i.e. sickle cell anemia\na)iii. nonsense mutations: code for a stop codon, which can truncate the protein\nb. insertions: add one or more extra nucleotides causing a shift in the reading frame (or frameshift)\nc. deletions: remove one or more nucleotides thus altering the reading frame (or frameshift)\n\n2. large scale mutations in chromosomal structure\na. amplifications or gene duplications: leading to multiple copies of chromosomal regions\nb. deletions of chromosomal regions: leads to loss of the genes coded; deletions in chromosome 5p causes cri-du-chat syndrome, deletions in chromosome 15q results in prader-willi syndrome\nc. translocations: interchange of genetic parts from non-homologous chromosomes thus bringing together separate genes to form functionally distinct fusion genes; translocations in chromosome 21 causes down syndrome \nd. inversions: reversing the orientation of a chromosomal segment thus bringing together separate genes to form functionally distinct fusion genes\n\nto detect small scale mutations affecting one or more nucleotides, a variety of tests can be done which in principle will test either the dna composition or the presence/absence of the gene products.\n\nlarge scale mutations in the chromosomal structures can be detected using karyotyping because the chromosomes with mutations would differ in sizes and shapes when compared to the standard. in general the chromosomes with deletions would be relatively smaller and chromosomes with additions would be relatively bigger than their counterparts, while chromosomes with either inversions and translocations would exhibit bridges and/or rings.
828336
Yes, of course it does. Breeding within a limited population always increases the incidence of recessive gene expression. Interestingly, a lot of these societies practice consanguineous marriage, which further amplifies the risk.
579995
Epigenetics are silent differences in DNA that can be passed on ie. methylations. So since the DNA sequence itself isn't changed it's a lot harder to tell if someone has a disease (if this change is contributing to a disease) by the methods used today of looking to see if the DNA has differenced in the sequence. This could explain how mutations get passed from generation to generation even if their actual DNA sequence looks like everybody else's. This is a fairly new area of biology being studied.
491168
PAGE gels only seperate based on size- in general, genes are the same size between humans, even if there is genetic variability-most genetic differences between human genes are substitution mutations, in which one base is changes for another (often this doesnt change the actual amino acid composition of the resultant protein because of redundancy in the codon system). So, since the size stays the same, the band will run to the same level.  In addition, single base changes will not show noticable differences in size on PAGE gels.  To determine single bp differences, you really have to run a sequencing gel and read the bases.  Keep in mind, outside the variable, non-coding regions, there is very very little difference between humans.
334406
Could just be mutations.
1047208
Biology has catalogued many traits produced by point mutations (changes at precise positions in an organism’s DNA)—bacterial resistance to antibiotics, for example. Mutations that arise in the homeobox (Hox) family of development-regulating genes in animals can also have complex effects. Hox genes direct where legs, wings, antennae and body segments should grow. In fruit flies, for instance, the mutation called Antennapedia causes legs to sprout where antennae should grow. These abnormal limbs are not functional, but their existence demonstrates that genetic mistakes can produce complex structures, which natural selection can then test for possible uses. Moreover, molecular biology has discovered mechanisms for genetic change that go beyond point mutations, and these expand the ways in which new traits can appear. Functional modules within genes can be spliced together in novel ways. Whole genes can be accidentally\nduplicated in an organism’s DNA, and the duplicates are free to mutate into genes for new, complex features. Comparisons of the DNA from a wide variety of organisms indicate that this is how the globin family of blood proteins evolved over millions of years. 11. Natural selection might explain microevolution, but it cannot explain the origin of new species and higher orders of life. Evolutionary biologists have written extensively about how natural selection could produce new species. For instance, in the model called allopatry, developed by Erns Mayr of Harvard University, if a population of organisms were isolated from the rest of its species by geographical boundaries, it might be subjected to different selective pressures. Changes would accumulate in the isolated population. If those changes became so significant that the splinter group could not or routinely would not breed with the original stock, then the splinter group would be reproductively isolated and on its way toward becoming a new species.\nNatural selection is the best studied of the evolutionary mechanisms, but biologists are open to other possibilities as well. Biologists are constantly assessing the potential of unusual genetic mechanisms for causing speciation or for producing complex features in organisms. Lynn Margulis of the University of Massachusetts at Amherst and others have persuasively argued that some cellular organelles, such as the energy-generating mitochondria, evolved through the symbiotic merger of ancient organisms. Thus, science welcomes the possibility of evolution resulting from forces beyond natural selection. Yet those forces must be natural; they cannot be attributed to the actions of mysterious creative intelligences whose existence, in scientific terms, is unproved.
499512
that's when an outside influence, like radiation or a glitch in the copying during cell division or something causes a change in the chromosome-- making it no longer an exact copy of the original. most of the time it's harmless or destructive; in the first case, it can be passed on but changes nothing, and in the second, the cell usually aborts or dies before it causes trouble. sometimes you get a cancer. sometimes you get a neat new adaptation.
1037230
This technique was considered a good one since it took all possible ways of aligning the sequences into account and the melting temperature would be a good average. However it is not considered the best approach these days since sequences can be computationally aligned. There is hardly any other approach used currently, however the sequences used for the comparisons are the major source of contention. Not all sequences evolve at the same rate. Some are too critical and changes can be lost if the result causes loss of function of the gene product/action. Finding the corresponding genes in more distant organisms can also be difficult. Some approaches have considered using non-coding sequences since these are not believed to be affected by evolution and all mutations in them would be retained faithfully. If one assumes a constant rate of background mutation, these mutations would indicate the age of the sequence lineage. However, these too are difficult for cross genera comparisons.
19329
maby a genome but making new ones is dangerous
81856
All answers are correct. The primary aminoacid sequence is changed which may have implications for the structure and funtion of the protein
264382
Organisms that are the best fit tend to survive longer and reproduce more, having more offspring and passing on their DNA to future generations.  If mutations occur in the DNA that makes the organism better able to survive, it's likely that it will be passed on.  If you look at organisms' DNA over time, you'd find the changes/mutations that have occured.\n\nThe above responder is absolutely incorrect about mutations: they CAN add nucleotides to the sequence of DNA. In fact, they can make 3 small-scale changes: point mutations (changing from one nucleotide into another), insertions (adding nucleotides), as well as deletions (removing nucleotides). I know this for a fact because we have just recently finished studying this exact subject matter in my biology class.  Also check out my source link and you'll find that out.
251117
Yes indeed even identical monozygotic twin siblings do have measurable phenotypic distinctions.  For example, their latent fingerprint patterns although similar are in fact different and easily distinguished by an expert examiner.  And  if they are both myopic their actual refractive correnctions will almost certainly be different. Rarely can identical twins exchange corrective glasses!  These subtle differences are the result of micoheterogeneity in the environment of the womb during embryogenesis. Subtle environmental alternations ultimately will be expressed as phenotypic differences.  Both embryos can not simultaneously occupy exactly the same space at the same time!  These subtle micro distinctions in their developing environment  affect their genetic expressions in slightly different ways!