Observed Genotype - the intermediate phenotypes are the...

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Observed Genotype Frequencies Allele count Allele frequency Expected genotytpe frequencies under H-W BB 0.71 142 B p = 156/200 = 0.78 p 2 = (.78) 2 = 0.61 Bb 0.14 14 B, 14 b 2pq = 2(.78)(.22) = 0.34 bb 0.15 30 b q = 44/200 = 0.22 q 2 = (.22) 2 = 0.05 Observed are different from expected, thus some force must be at work to change frequencies. NATURAL SELECTION Selection occurs because different genotypes exhibit differential survivorship and/or reproduction. If we consider a continuously distributed trait (e.g., wing length, weight) with a strong genetic basis, the response to selection can be characterized by where in the distribution the "most fit" (greatest survivorship&reproduction) individuals lie. If after selection one extreme is most fit this is directional selection ; if
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Unformatted text preview: the intermediate phenotypes are the most fit this is stabilizing selection ; if both extremes are the most fit this is disruptive selection . R. A. Fisher proposed a simple bookkeeping, or population genetics, approach for one locus with two alleles: we have AA, Aa and aa in frequencies p 2 , 2pq, q 2 . Define l ii as the genotype-specific probability of survivorship, mii as the genotype-specific fecundity. We build a model that will predict the frequencies of alleles that will be put into the gamete pool given some starting frequencies at the preceding zygote stage; Genotypes Zygote -----> -----> Adult-----> -----> Gametes AA p 2 l AA p 2 m AA l AA p 2 Aa 2pq l Aa 2pq m Aa l Aa 2pq aa q 2 l aa q 2 m aa l aa q 2...
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