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where Ne is the genetic effective population size and r is the recombination fraction per generation (Hill & Robertson 1968; Ohta & Kimura 1969; the basis of this type of equation is derived in Chapter 4). As shown in Fig. 2.22, when the product of Ne and r is small, chance sampling contributes to maintaining some gametic disequilibrium since only a few gametes contribute to the next generation when Ne is small or only a few recombinant gametes exist when r is small. The lesson is that D as we have used it in this section assumes a large population size

(similar to Hardy-Weinberg) so that actual gamete frequencies approach those expected based on allele frequencies, an assumption that is not always met in actual populations.

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