14_Population_subdivision(1).pdf - FRSC-BIOL 3700 14 – Population subdivision Aaron Shafer Last Lecture ● Calculating inbreeding Last Lecture ●

# 14_Population_subdivision(1).pdf - FRSC-BIOL 3700 14 –...

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FRSC-BIOL 3700 14 – Population subdivision Aaron Shafer

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Last Lecture Calculating inbreeding
Last Lecture Impact on genotype frequencies AA = p 2 + pFq Aa = 2pq(1 -F) aa = q 2 + qFp F ROH and F h

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Population subdivision Many species occupy such vast geographic areas or have such effective barriers to migration that they cannot behave as a single, randomly mating population In such cases, there will be genetic differentiation between subpopulations , which leads to departures from Hardy- Weinberg for the entire species.
Population subdivision - humans

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Population subdivision - giraffes
Population subdivision - mockingbirds

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Population subdivision In the case where there is random mating within each subdivision, the genotype frequencies for the entire species are described by a new incarnation of F called F ST The deviation from random mating that is F ST reflects the difference between the subpopulation (S) and the total population (T). This is an extension of last lectures inbreeding formulas, notably hierarchical F statistics
Two populations HWE HWE Genotype frequency for entire species is simply the average of the two patches: (1 /16 + 9/16) / 2 = 5 / 16

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Two populations HWE HWE Expected genotype frequency of species under HWE; important to note that while each subpopulatin is meeting HW expectation, the entire species is not (because of subdivision!) In this case there are too many homozygotes.
Two populations The excess of homozygotes requires an F ST of 0.25 (or 1/4). How do we know that? Let’s revisit our equation from last lecture: 2pq(1- F ) = 3/8 Rearrange and solve: (1 – F )/2 =3/8 = 1/4 BUT we have no idea if this excess in heterozygotes is due to inbreeding OR subdivision OR something else!

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