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Genetics (week 9): Population Genetics


complex issue of how genes are distributed in populations
typical genotype??
heterozygotes/carrier prevalence?
pop freq of genetic dz?
factors affecting freq of genes in pop over time?
if you can do Q4 on p116 then you got it

biological pops have 3 genetic characteristics:
1) a gene pool = sum total of all allels in reproductive gametes, can be mathematically modeled
2) allelic frequencies
3) genotypic and phenotypic frequencies

**Hardy Weinberg equilibrium
= balanced state of gene pool, allelic freq remains constant
**requires 5 conditions: no mutation, no migration, no assortative mating, no selection, no genetic drift
p112 explains how this is met in human pop
mutations infrequent and rarely stick around past a generation or three
migration concerns mediated by size of pop, big pops more stable
random mating: based on "a few superficial characteristics"--he discounts sense of smell as gene detection
selection: we have it easy, environment doesn't pick off humans much
genetic drift happens in small pops but hardly detectable in large, allelic freq changes are minor fluctuation

modelling based on HW equilibrium
p = frequency of A
q = frequency of a
p + q = 1, or if 3 alleles call the 3rd r and p + q + r = 1
genotype frequencies: Aa = 2pq, AA = p squared, aa = q squared
** pq x pq --> **p2 + 2pq + q2 = 1 = HW equilibrium for single gene 2 allele system***
3 allelic system, genotypes = (p+q+r)squared =1, or p2+q2+r2+2pq+2pr+2qr=1
4 alleles add s to the series
(binomial theorem)
see 3 examples p114, #1 is most important one to know

do problems!!!

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