{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

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

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

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...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online