To begin we need to understand some simple population genetic

# To begin we need to understand some simple population genetic

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To begin we need to understand some simple population genetic "bookkeeping." Consider a locus with two alleles (alternative forms of the DNA sequence that "reside" at that locus, e.g., one from mother other from father). Now consider a population of N individuals (N=population size); this means that there are 2N alleles in the population. We can thus talk about genotype frequencies and allele frequencies . In a population of N = 100 individuals, if there are 25 AA, 50 Aa and 25 aa, then the genotype frequencies are f(AA) = 0.25, f(Aa) = 0.50 and f(aa) = 0.25. If we count up the individual alleles there are 200 of them (because there are 100diploid individuals). Hence to determine the frequency of the "A" allele we have to count each individual "A" allele that is specified in each diploid genotype. We get
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Unformatted text preview: f(A) = (25+25+50) / 200 = 0.5. We generally refer to the frequency of the "A" allele as f(A) = p; the frequency of the "a" allele is f(a) = q. Note that p = (1-q) because the sum of the allele frequencies must be 1.0. Common "language errors" in learning population genetics are to refer to the "p" allele when you really mean the "A" allele, or to say "the frequency of the p allele" when you really mean: ". ..p, the frequency of the "A" allele. .." Got it?? Good. Since evolution is change in the genetic makeup of a population over time, a general approach to modeling this is to determine the allele and genotype frequencies in the next generation (p t+1 ) that result from the action of a force on those frequencies in the current generation (p t ). Thus : p t-> evolution happens -> p t+1...
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