LIFESCI 1 Lecture Notes - Lecture 5: Genetic Drift, Allele Frequency, Natural Selection
Genetic Drift
• Genetic drift and gene flow are not the same thing
• Genetic drift is due to sampling error
• Drift is due to random chance
• If the frequency of an allele is 100% or 1, we say that allele has become fixed
• If 0, it is lost or extinct
• All (finite) populations go through some genetic drift
• But drift is especially important in small populations
• Drift is not just theoretical
• Why don’t allele populations drift back? → “Once the allele is lost, how would you get it
back?” Mutation
• Genetic Drift Question → B. 0% : If an allele goes to fixation, 100% of the individuals
have that genotype, there is no variation from what you started with (therefore 0%)
• Effective Population size : a measure of how much drift a population is experiencing.
• Why is Ne smaller than the actual population size? →”If an allele is fixed, than everyone
is going to be homozygous”, We’re making some assumptions with nonrandom mating.
Nonrandom Mating
• 2 types: Inbreeding, or regular systems of inbreeding
• Sexual selections and regular mating systems
• Violating only the HW assumption of infinite population size results in genetic drift
• Drift acts as a kind of inbreeding
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