Genetic drift
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What is genetic drift?
Non-adaptive, random genetic changes between generations
What are the assumptions of the Hardy-Weinberg theory?
• Either no selection or that selection is constant • No immigration/emigration • Negligible effect of mutations • Population size is large
What is the problem with deterministic models of evolution?
• Real world is stochastic - Chance always intervenes
How could non-selective forces lead to the loss of a gene?
Random sampling, especially if sampling is small, can induce variation in gene frequencies between generations Can loose genes due to a lack of gamete success
What conclusions can we draw from genetic simulations?
• Genetic drift happens more quickly at smaller populations • Even in large populations fixation is inevitable but happens over more generations • Allele that goes to fixation depends on the initial concentrations in the population • Near-neutral genes always become fixed, only mutation/migration causes counter-fixation
Why is N not equal to Ne?
Population size not equal to effective population size • Territorial/sexual selection • Sex ratio biases towards rarer sex • Variable fertility • Negative effect between N & Ne
What is the most common way to estimate Ne?
Inferring the number of breeding adults from hypervariable genetic markers
When does selection win out over drift?
When 4Ne.S»_space; 1
What is the effect of inbreeding?
Causes increase in the frequency of deleterious recessives