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# HO-25 - Population genetics the genetic basis for evolution...

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BIO 320 Reading: Ch 21.1 - 21.2, lecture 25 Problems: Question bank E & text problems 21.1-5, 10, 13, 17-8, 20-21. Population genetics: the genetic basis for evolution Final exam: Javits 100, Thursday May 15, 2:00 - 4:30pm. the “neo-Darwinian synthesis”: Evolution can be understood in terms of change in allele frequency After the rediscovery of Mendel's laws (and considerable argument...) • Part I: why allele frequencies don‘t change, except in the case of... • Part II: when allele frequencies do change Part I. Why allele frequencies don't change: Hardy-Weinberg (H-W) equilibrium . GENE POOL (NO DIVING) Aa aa AA Allele frequency : at any locus, the proportion of one allele among all copies of the locus in a population A. Finding allele frequencies (p, q) from genotype frequencies: • individuals of all genotypes have an equal chance of contributing to gene pool ( no selection ) and... • no genes come from outside the population ( no migration ).. • and gametes are chosen independently of each other ( random mating )... • and there is no mutation... • in a large population (much larger than shown here), and... IF... THEN.. The frequencies of the genotypes in the next generation are given by: p 2 2pq q 2 • 1 locus • 2 alleles: A & a • all 3 genotypes distinguishable • total # of alleles in population = 2x(# of individuals). p = freq. ( A ) = # [ AA ] + 1/2 # [ Aa ] total # of individuals q = freq. ( a ) = # [ aa ] + 1/2 # [ Aa ] For two alleles: p + q = 1 or q = 1 - p (Compare to a cross of 2 individual heterozygotes, where all gamete frequencies = 1/2) A a A a p q p q AA Aa aA aa p 2 q 2 pq pq B. Combining allele frequencies to generate the next generation's genotype frequencies.

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HO-25 - Population genetics the genetic basis for evolution...

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