Lecture 8 - Non-random mating

Lecture 8 - Non-random mating - 1 Lecture 8 - Non-Random...

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1 Lecture 8 - Non-Random Mating and its Consequences - Mating is usually not random (even in self-fertile hermaphrodites). Causes of non- random mating are: inbreeding per se (mating with an individual with whom you share more genes than random), assortative mating (e.g., choosing a mate based on some phenotypic attribute), geographic proximity. - The single-locus result of non-random mating is to cause the population to deviate from Hardy-Weinberg equilibrium. - If individuals that share more genes than expected are more likely to mate, the result is an excess of homozygotes over the H-W expectation (this is common). Consanguinous mating, positive assortative mating, geographic isolation produce this result - If individuals that share more genes than expected are less likely to mate than expected, excess of heterozygotes (this is less common) Self-incompatibility mechanisms in plants, incest taboos in humans produce this result - Define f as the probability that two gene copies are Identical by Descent at some arbitrary time in the past (we are not restricting the status of I by D to the previous generation as we did previously [Figure]). An interesting way to think of f is as the "Probability of Homozygosity due to Special Circumstances" (PHSC, pronounced phonetically). Note that in the lecture in which I introduced the notion of identity by descent (which I designated f ), the "special circumstance" is finite population size and the probability of identity by descent in the previous generation is 1/2N. Generalized H-W Genotype A1A1 A1A2 A2A2 frequency p 2 (1- f ) + p f 2 pq (1- f ) q 2 (1- f ) + q f Note there are two ways to be homozygous A1A1. First, the two gene copies can by I by D with probability f . Among all pairs of genes that are I by D,
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Lecture 8 - Non-random mating - 1 Lecture 8 - Non-Random...

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