Topic 8 Genetic Drift

-Chance fluctuations in allele frequencies as a result of randomly sampling gametes in each generation

• direction of genetic drift is RANDOM (cannot be predicted) • magnitude of drift depends on population size. The smaller the pop’n, the larger the potential for change (from one gen to another) • causes pop’ns to genetically diverge from each other • will reduce genetic variability w/in a pop’n over time (in absence of anything else)–> fixation of alleles over time causes h=0

changes in allele frequencies among populations such that the populations become less similar in allelic composition

divergence as a result of physical barriers

ONLY gives us the probability that two randomly chosen alleles will be autozygous -vs. F (inbreeding coefficient): gives the prob. that randomly chosen alleles will be autozygous AND the fractional reduction in heterozygosity in comparison to a panmictic pop’n

Nc is the pop’n size which has been estimated by an enumeration method -rarely if ever equal to effective pop’n size (Ne)

• Ne is the size of a pop’n with: a) equal numbers of males and females b) panmictic c) and constant pop’n size over time that will undergo reductions in genetic variations at the SAME RATE as our census pop’n (due to drift alone) -or Ne is the size of a pop’n that will undergo the same rate of increase in Fi over time as our census pop’n

• when the pop’n size suddenly drops down in one generation • form of genetic drift • reduces genetic variability and increases Fi

• a reduction in genetic variation as a result of a population being founded (started) from a small # of colonizing indiv. from a parent pop’n • sampling error • reduced variability and diff allele freq’s • same effect as bottleneck