E not 50m 50f effective size usually census size size

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Unformatted text preview: a pop’n • Variation in number of progeny among individuals – Stochastic differences in the genetic contribution of individuals • Effective size (Ne) = number of adults that breed • Unequal sex ratio (i.e. not 50m : 50f) – Effective size usually << Census size – Size of an ideal population (every adult reproduces) in which genetic drift equals the rate in the real population • Overlapping generations – Mating between offspring and parents • Rate of drift = rate of decline in heterozygosity over time • Fluctuations in population size • Effective size is most important for evolutionary analysis – Population bottlenecks – Ne is a harmonic mean across generations • Example: pop’n with 10,000 adults – But only 1000 of them mate at random and reproduce – N = 10,000 … Ne = 1000 Consequently, the number of individuals making genetic contributions to the next generation is almost always lower than the total census number of individuals. 19 20 -Not everyone has the same number of offspring -Individuals making genetic contribution is ALWAYS lower!! Two views of domestication Ne << N Past • This happens even in the absence of selection Ne at T1 Ne at T1 Ne at T1 + Versus... TIME • Natural or artificial selection reduces Ne even further – Deterministic differences in the genetic contributions of individuals • Ne can be measured as a “species average” across the genome Bottleneck lasting t generations t t Present Ne at T2 Ne T1 > Ne T2 • Ne can also be measured for each gene separately Bottleneck affects the entire genome. All loci are affected – Selection on a given gene will lower its Ne 21 Ne at T2 Ne at T2 Ne T1 >>> Ne T2 Ne T1 > Ne T2 Bottleneck produces genome wide reduction in Ne for all loci. Selected loci show even greater reduction in Ne compared to the rest of the genome. 22 -Ancestral population experiences a bottleneck that affects ALL genes and reduces the Ne of ALLLLLL loci -Loci that are selected for or against (via NS) show even MORE reduction in Ne Results for maize & teosinte Key idea • Purely demographic consequences of bottleneck have genome wide effects of reducing Ne • Artificial selection should lead to addit...
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This document was uploaded on 01/27/2014.

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