Genetic Drift
The intrusion of random events into the genetics of a population/change in allele frequency due to random sampling.
What does genetic drift lead to?
It leads to changes in allele frequencies but does not lead to adaptation.
What does genetic drift result from in the HW model? How?
From violation of the assumption of infinite population size. In a small population, chance events produce outcomes that differ from theoretical expectations.
Selection vs. Genetic Drift
Selection is differential reproductive success that happens for a reason.
Genetic drift is differential reproductive success that just happens.
Relationship between genetic drift and population size
Indirect. As genetic drift increases, population size decreases. The sampling error diminishes as sample size increases.
Founder effect
When a population is founded by a small number of individuals, it is likely that chance alone (genetic drift) will cause the allele frequencies in the new population to be different from the source populations.
3 things to remember for genetic drift
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What will happen if genetic drift is the only evolutionary mechanism at work?
Then eventually one of the alleles will drift to fixation.
How do you determine the probability that any given allele in a population will be the one that drifts to fixation?
It is equal to that allele's initial frequency.
Relationship between genetic drift and heterozygosity
Genetic drift decreases heterozygosity
Heterozygosity
The frequency of heterozygotes in a population
What is the Wahlund effect?
Finding more homozygotes than you would predict based on the random mating of a population. This is because the population is structured and these populations have a loss of heterozygosity because of genetic drift.
Effective population size
The size that the population (actually larger) is really behaving like
What can make the population behave smaller (i.e. have a smaller effective population size)?
- Unequal sex ratio
(example of fishing for crabs and tossing female back into the ocean).
- Variation in reproductive success