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Unformatted text preview: HardyWeinberg Theorem 320 20 x2 HardyWeinberg Theorem HardyWeinberg Theorem Note Same H.W. Frequencies (2 alleles) Note how Genotype Frequencies are 100% a function of previousgeneration Allele Frequencies . This is precisely what the H.W. equation tells us. It is the default evolutionary assumption (i.e., no evolution is occuring) H.W. Assumptions To assume HardyWeinberg equilibrium all of the following must be true: 1. The population must be very large (no sampling error/genetic drift) 2. There must be no net mutation 3. There must be no natural selection (though as we will see that this assumption can be temporarily suspended in the course of using the Hardy Weinberg theorem) 1. No migration between populations 2. Random mating (equivalent to mixing all sperm and eggs in population into a common bucket to foster fertilization) In other words, no mechanisms that can affect genetic structure i.e., allele or genotype frequenciesmay be operating H.W. Equilibrium If no mechanisms that can affect genetic structure are operating, then HardyWeinberg genotype frequencies will be established in a single generation And these frequencies will persist indefinitely (I.e., so long as there are no mechanisms operating that can affect genetic structure) Solving H.W. Problems Work with Decimals , not percentages, not fractions, not absolute numbers Convert Phenotypes to Genotypes , whenever you are given phenotype information you should be pondering (i) how can I convert phenotypes to genotypes? and (ii) how can I convert known phenotype frequencies to genotype frequencies? Convert Genotypes to Alleles , once you know genotype frequencies it should be trivial to convert to allele frequencies: dont let this step trip you up Convert Alleles to Genotypes , if you know allele frequencies, but not genotype frequencies, then chances are you will need to figure out the latter Incorporating Selection , usually selection only operates at the diploid stage make sure frequencies always add up to one Practice, Practice, Practice, Practice, Practice! Working with Decimals Convert percentages to decimals (I.e., by dividing by 100): 25% 0.25 Convert fractions to decimals (I.e., by dividing by the denominator): 0.25 Convert absolute numbers to decimals (I.e., by dividing number by total): 60/240 0.25 Many a HardyWeinberg solution has been tripped up by not employing decimals, i.e., by not employing frequencies E.g., 25% x 25% = 625%! (which is incorrect) E.g., 0.25 x 0.25 = 0.0625! (which is correct) Yes, 25/100 x 25/100 = 625/100/100 = 0.0625 But isnt that absurdly complicating??? Phenotype Genotype Phenotype to Genotype conversions are going to depend on the genetics of your locus Always in these problems genotypes will be diploid If alleles have a dominancerecessive relationship, then the heterozygote will have the same...
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 Spring '08
 Swenson
 Biology, Evolution

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