What is epistasis? plz explain it with examples clearly?
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Epistasis refers to the phenomenon where one or more genes will mask the effects of another gene in a different position on a chromosome (or locus). This shouldn't be confused with dominance though where the interaction takes place in the same locus.\n\nSimple Example: The gene that causes Albinism hides the gene controlling the color of a person's hair.\n\nAnother Example: Bombay Phenotype - This involves the ABO Blood group system. They lack a protein called the H antigen which is used to form the A and B antigens. So even though they may have A or B genes, they appear to be blood group O because of the lack of H antigens.
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DNA is a way of storing information.  But that is far from intelligence.  Nothing senses changes in the environment and *decides* that it needs to change the organism to survive.\n\nYou are on the right track that there is an *element* of "luck" involved.    Randomness creates *variation*.  But there are two corrections you should know:  (1) Mutation is not the only source of randomness; and (2) Randomness is not the only thing driving evolution ... i.e. EVOLUTION IS NOT BLIND LUCK.\n\n1. Random mutations are improbable, but given huge numbers of replications, and huge amounts of time, there are *many* chances for mutations to occur, and those that produce some slight advantage tend to get propagated slightly better into future generations.  \n\nBut the invention of sexual reproduction took that randomness to a whole new level.   DNA from two different individuals could produce *huge* numbers of different combinations.  This allows improvements to propagate much faster into future generations, and allowed much faster adaptations to a changing environment.\n\n2. It's really important to know that EVOLUTION IS NOT JUST RANDOMNESS (BLIND LUCK).  Evolution is driven by 3 ingredients: variation + selection + time.  Randomness produces the *variation* ... but the selective pressures are NOT random.  \n\nFor example, a mammal may have several litters of offspring, say 20 in total.  Randomness produces the *variation* that some of these will be more hairy than their siblings.  But there is *nothing* random about the fact that those offspring with more hair may survive better in a colder environments and therefore produce more babies.  (E.g. if the environment is getting colder, or if some members want to, say, push a little further north.)  Add the ingredient of *time* and a much hairier subspecies can arise and get separated from the parent species ... and even more *time* and the subspecies can completely lose the ability to mate with the parent species, and you have two different species.\n\nSummary: randomness supplies the sparks of evolution, but selective pressures in the environment + time, provide the fuel.
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Those terms are for individual genes, not people. A gene is made up of a pair of alleles, one from each gamete. These alleles can be one of many variations. If the alleles are identical, the gene is homozygous.
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Monohybrid inheritance is the inheritance of a single characteristic. The different forms of the characteristic are usually controlled by different alleles of the same gene. For example, a monohybrid cross between two pure-breeding plants (homozygous for their respective traits), one with yellow seeds and one with green seeds, would be expected to produce an F1 (first) generation with only yellow seeds because the allele for yellow seeds is dominant to that of green.\n\nSource:\nhttp://en.wikipedia.org/wiki/Monohybrid
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are you talking about genes? the complex arrangement of genes in numerous chains make up the characteristics of primates and most of all duel-reproductive organisms. out of the thousands, only a few have been mapped or pulled apart into single strands. the UCLA medical school has links to genetic mapping web sites. very cool!
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#1)  Primarily by mutation.  A mutation must occur a germ cell (cells that produce sperm and eggs).  This can produce progeny with novel traits.  This is fairly rare event (one out of every billion nucleotides copied during meiosis).  Our body has ways of fixing these errors, but this is the biological basis of evolution.\n#2)  By crossing over.  During meiosis, parental chromosomes will swap pieces with each other.  For example, I used pieces of my mother's chromosome #1 and my father's chromosome #1 when I made the chromosome #1 that I passed to my daughter.  I passed a different combination of pieces to construct a chromosome #1 for my second daughter.\n#3)  By independent assortment during meiosis.  So not only did I make novel chromosomes out of pieces of my parents chromosomes, but I created a gamete using a unique combination of my mother and father's chromosomes.  For example I might have used chromosomes 1-11 of my father's (with pieces of my mother's chromosomes 1-11) and numbers 12-22 of my mother's (with pieces of my father's chromosomes 12-22).  For my second daughter it could have been totally different.  It is a unique situation each time!  No two gametes are the same.
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Phenotype\nThe phenotype of an individual organism is either its total physical appearance and constitution or a specific manifestation of a trait, such as size, eye color, or behavior that varies between individuals. Phenotype is determined to some extent by genotype, or by the identity of the alleles that an individual carries at one or more positions on the chromosomes. Many phenotypes are determined by multiple genes and influenced by environmental factors. Thus, the identity of one or a few known alleles does not always enable prediction of the phenotype.\n\nNevertheless, because phenotypes are much easier to observe than genotypes (it doesn't take chemistry or sequencing to determine a person's eye color), classical genetics uses phenotypes to deduce the functions of genes. Breeding experiments can then check these inferences. In this way, early geneticists were able to trace inheritance patterns without any knowledge of molecular biology.\n\nPhenotypic variation (due to underlying heritable genetic variation) is a fundamental prerequisite for evolution by natural selection. The fitness of an organism is a high-level phenotype determined by the contributions of thousands of more specific phenotypes. Without phenotypic variation, individual organisms would all have the same fitness, and changes in phenotypic frequency would proceed without any selection (randomly).\n\nThe interaction between genotype and phenotype has often been conceptualized by the following relationship:\n\ngenotype + environment → phenotype \n\nA slightly more nuanced version of the relationships is:\n\ngenotype + environment + random-variation → phenotype \n\nAn example of the importance of random variation in phenotypic expression is Drosophila flies in which number of eyes may vary (randomly) between left and right sides in a single individual as much as they do between different genotypes overall, or between clones raised in different environments.\n\nA phenotype is any detectable characteristic of an organism (i.e., structural, biochemical, physiological and behavioral) determined by an interaction between its genotype and environment (see genotype-phenotype distinction and phenotypic plasticity for a further elaboration of this distinction).\n\nAccording to the autopoietic notion of living systems by Humberto Maturana, the phenotype is epigenetically being constructed throughout ontogeny, and we as observers do the distinctions that define any particular trait at any particular state of the organism's life cycle.\n\nThe idea of the phenotype has been generalized by Richard Dawkins (in The Extended Phenotype) to mean all the effects a gene has on the outside world which may influence its chances of being replicated. These can be effects on the organism in which the gene resides, the environment or other organisms.\n\nand\n\nGenotype\nThe genotype is the specific genetic makeup (the specific genome) of an individual, in the form of DNA. Together with the environmental variation that influences the individual, it codes for the phenotype of that individual. Non-hereditary mutations are not classically understood as representing the individuals' genotype. Hence, scientists and doctors sometimes talk for example about the (geno)type of a particular cancer, thus separating the disease from the diseased. While codons for different amino acids may change in a random mutation (changing the sequence coding a gene), this doesn't necessarily alter the phenotype.\n\nTypically, one refers to an individual's genotype with regard to a particular gene of interest and, in polyploid individuals, it refers to what combination of alleles the individual carries (see homozygous, heterozygous). Any given gene will usually cause an observable change in an organism, known as the phenotype. The terms genotype and phenotype are distinct for at least two reasons:\n\n1. To distinguish the source of an observer's knowledge (one can know about ge
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An allele.  Alleles can be dominant or recessive.
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A homozygote's cells are diploid or polyploid and have the same alleles at a locus (position) on homologous chromosomes. When an organism is referred to as being homozygous for a specific gene, it means that it carries two identical copies of that gene for a given trait on the two corresponding chromosomes (e.g., the genotype is AA or aa). Such a cell or such an organism is called a homozygote.\n\nA homozygous dominant genotype occurs when a particular locus has two copies of the dominant allele (e.g., AA). A homozygous recessive genotype occurs when a particular locus has two copies of the recessive allele (e.g., aa). This can occur when both parents carry at least one copy of the allele.\n\nPut simply: Homozygous is just having two of the same alleles.
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dr d is correct.\n\nIt is transfer of genes within a generation, as compared to transfer from the parental generation to the offspring generation; that is vertical gene transfer between generations.\n\nIf genes are picked up from a cell in some way, and put into other cells (not involving cell division), then the genes have been transferred "horizontally".\n\nAn example is when a bacterium carrying a certain plasmid grows a "sex pilus", which then connects with the cell wall of a bacterium that does not carry that plasmid.  It will inject a copy of the plasmid, via the sex pilus, and the recipient has then become a carrier, too.  These plasmids often carry extra genes, as well as those coding for this ability.  These phenomena are sometimes considered to be similar to sex, but are really more like catching a virus!
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Each chromosome in your body has an "identical pair"- there are two chromosomes that code for the same functions- one from your mother and one from your father.\n\nBecause they come from two sources, they are coding for the same functions, but may code differently for them (ie blue eyes as opposed to brown eyes).\n\nDuring prophase one, each chromosome duplicates into two sister chromatids joined by a centromere, and then the double stranded chromosome finds it's partner which is coding for the same thing (just came from the opposite parent), and is also double stranded.  Now you have a 4 stranded tetrad.\n\nGenetic variability comes from crossing over.  This is where the two chromatids closest together in the tetrad exchange some genetic information.\n\nFor example, two of the chromatids code for blue eyes, brown hair and shortsightedness.\nThe other two chromatids code for brown eyes, red hair and normal vision.\n\nDuring crossing over one chromatid from each pair forming the tetrad literally have ends "crossing over" and bits of information are exchanged.\n\nAfter crossing over, you have 4 chromatids with unique codings.  Using the example above, we may now have:\n-blue eyes, brown hair, shortsightedness\n-blue eyes, red hair, normal vision\n-brown eyes, brown hair, shortsightedness\n-brown eyes, red hair, normal vision\n\nWe now have genetic variability in each gamete produced from this meiotic division.
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A genotype is the actual genetic code of an organism, the sequence of the base pairs on the DNA. The phenotype is what those genes actually express, what you would see if you looked at the organism.\n\nSay there's a gene that controls the color of a mouse's fur. We'll call the dominant form of the gene which gives brown fur, B. The recessive form, for white fur, will be b.\n\nA mouse gets one copy of the gene (called an allele) from each parent, for a total of two. That means there are three combinations of alleles: BB, bb, and Bb. A mouse with two recessive alleles will be white, and a mouse with two dominant alleles will be brown. A heterozygous mouse (with one dominant and one recessive copy) will also be brown.\n\nGenotype          Phenotype\nbb                White\nBB                Brown\nBb                Brown\n\nSo even though the BB and Bb mice have different genotypes, they have the same phenotype.\n\nIn the example above, the phenotypic ratio would reflect the amount of mice of a different color in a population. For example, if you crossed two heterozygous mice, the brown to white ratio of the offspring would be 3:1. The genotypic ratio, reflecting the genetic code of the offspring (BB to Bb to bb), would be 1:2:1.
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Then defend it... I say that there is no way that a random chance process could have formed life forming proteins and DNA with their unique chirality. If proteins and DNA were formed by chance  each and every one of the components would be a 50/50 mixture of the two optical isomers. This is not what we see in natural proteins or in natural DNA. How can a random chance natural process create proteins with thousands of "L" molecules, and then also create DNA with billions of "R" molecules? Does this sound like random chance or a product of design? Even if \nthere were a magic process to introduce chirality, it would only create one isomer. If such a process existed, we do not know anything about it or how it would work. If it did exist, how were compounds with the other chirality ever formed? Even if there were two magical processes, one for each isomer, what determined which process  was used and when it was used, if this was a random chance natural process? The idea of two processes requires a controlling mechanism, and this kind of control is not possible in a random chance natural process.\nYou are an intelligent man alot smarter than a mere theist so I don't think I need to explain chirality more thoroughly. You just need to defend your statement... Too bad you can't now that you have this informant ion.....   Jim
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Here's a little known fact - the theory of natural selection - very few on YA can describe it correctly yet it's very simple:\nThere are just 3 assumptions:\n\n1. Individual members of a species are not always exactly alike. A population of similar organisms displays variability.\n\n2. Organisms possess some mechanism by which offspring tend to be like their parents. That is, individual traits are heritable.\n\n3. Totally unrestricted breeding doesn't happen. No population can reproduce forever without limit. So clearly there must be some force at work to reduce populations.\n\nFrom these assumptions Darwin concluded the theory of natural selection - some of the variations between individuals are inherited by their offspring, and, in a world where not everyone can survive, some of these inherited characteristics give some individuals a better chance of survival.
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EEEEH. I'm not really good with this mumbojumbo stuff but here is a site on genotypes and stuff. -> http://janis7hepc.com/Genotypes.htm <-
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get different genetics
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When Mendal observed that his 7 traits assorted independantly of each other in peas, he assumed that all traits assorted independantly of all other traits, and made that a law of inheritance.\n\nWell, we know know that's wrong.  We observe that while many pairs of traits assort independantly, many other pairs do not.  Thomas Hunt Morgan's lab first observed that fuit fly eye color was linked to fly sex.  Other people observed that other pairs of traits were not totally completely linked, but that they were not totally independant either.  When two traits were found to not assort completely independantly, the term used to describe that situation was "linkage".\n\nWe now know that linkage happens because genes aren't floating around as perfect little gene spheres, bobbing around the nucleus.  They are arranged "like pearls on a string" on chromosomes.  So genes that are on the same string will not assort independently.  Meiosis will sometimes split them, sometimes not, depending on how close the genes are to each other.  They are physically linked, and we call the dependant assortment linkage too.