Bio 321 F13 lecture 8 v2

To 100 for neutral alleles the

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Unformatted text preview: iU and homozygosity •  each subpopulaGon “is likely close to HWE because Drosophila tends to avoid inbreeding” •  if this is true, the excess homozygosity in the metapopulaGon is mostly in the form of between- populaGon variaGon –  many populaGons are p=0 or q=0 •  in the enGre metapopulaGon, the overall frequencies of alleles p, do not change, as long as there are enough subpopulaGons –  effects average out F- staGsGcs •  Sewall Wright noGced that driU and inbreeding had similar effects on heterozygosity in metapopulaGons •  developed three interrelated F- staGsGcs to describe how allele frequency variaGon is parGGoned within and between subpopulaGons of a metapopulaGon image_n/nfgz001.gif table 3.1 allele frequencies genotypic frequencies within subpopulaGons piqi (vary from 0 to 1) p2, 2pq, q2 (HWE) (if A is fixed: p2=1, 2pq=q2=0; sGll HWE) overall metapopulaGon p, q =p0, q0 if no selecGon excess homozygosity due to fixaGon by geneGc driU HI •  observed heterozygosity in subpopulaGons •  calculated as we have previously done •  ideally, use mulGple loci –  average over all loci –  or can calculate HI and F- staGsGcs for individual loci HS •  expected heterozygosity with random maGng in a subpopulaGon •  previously we have called this H0 •  =2piqi HT •  expected heterozygosity if there were random maGng over the enGre metapopulaGon –  i.e. if the metapopulaGon were panmic?c •  = 2p0q0 = 2pq F- staGsGcs for 3 hierarchical levels use frequencies •  FIS = (HS- HI) / HS •  measures proporGonal reducGon of heterozygosity in subpopulaGons due to inbreeding •  same as F, which we saw previously •  bars denotes averages across subpopulaGons F- staGsGcs for 3 hierarchical levels use frequencies •  FST = (HT- HS) / HT •  measures proporGonal reducGon of heterozygosity in enGre metapopulaGon due to differenGaGon among subpopulaGons –  relaGve to expectaGon if there were no populaGon subdivision •  HS is averaged across all subpopulaGons •  meaningless for one subpopulaGon •  HT is expected heterozygosity across enGre metapopulaGon •  also = V/ pq more on FST V =variance in allele frequencies among subpopulaGons if all subpopulaGons have exactly the same allele frequenci...
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This note was uploaded on 10/01/2013 for the course BIO 321 taught by Professor John during the Spring '12 term at SUNY Stony Brook.

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