L05-Genetic Drift

• generates genetic variation


  Mutation
• changes expression of genes

  Epigenetic modification
• causes fluctuation in allele frequencies and can reduce genetic variation

  Genetic Drift
• acts on genetic or epigenetic variation in a population

  Natural selection
• ____genetic or epigenetic variation, Natural selection cannot occur

  without
• can act as a homogenizing force

  Migration
• If two populations are different, migration between them can reduce the differences


  True
• A population could go out of HW equilibrium with a lot of migration


  True
• could introduce genetic variation into a population


  Immigration
• could reduce genetic variation in a population

  Emigration
• Genetic drift and inbreeding could generate new gene interactions


  True
• These new gene interactions (epistasis caused by new recombinations) are the main substrate for selection

  True
• Changes in allele frequency from one generation to the next simply due to chance (sampling error)

  Random Genetic Drift
• Random genetic drift is a NON ADAPTIVE evolutionary force


  True
• Darwin did not consider genetic drift as an evolutionary mechanism, only natural selection


  true
• Genetic Drift happens when populations are limited in size, violating HW assumption of infinite population size


  True
• When population is large, chance events cancel each other out


  True
• When population is small, random differences in reproductive success begin to matter much more


  True
• In evolution, when we talk about population size, we mean

  effective population size
• The concept of effective population size Ne was introduced by Sewall Wright, who wrote two landmark papers on it (Wright 1931,1938)


  True
• The population sized based on its genetic variation


  Effective population size
• The effective population size is almost always either equal to or less than census population size (N)

  True
• The effective population size is usually smaller than the real census population size because not everyone breeds and leaves offspring


  True
• Unequal sex ratio, variation in number of offspring, overlapping generations, fluctuations in population size, nonrandom mating could lead to an effective population size that is smaller than the census size

  True
• Ne(Effective population size) is the actual unit of evolution, rather than the census size N


  True
• Only the alleles that can actually get passed onto the next generation count in terms of evolution...the individuals that do not mate or have offspring are evolutionary dead ends

  True
• If a population is completely inbred, its Ne=1 or extremely low, even if the census size is large


  True
• Selection happens when some survive for a reason: better adapted


  True
• Genetic drift is just a numbers game. Which gamete gets fertilized, which allele gets passed on is RANDOM
• If population size is reduced at the allelic level: random fixation of alleles (loss of alleles)
• If population size is reduced at the genotypic level: loss of heterozygosity (because of fewer alleles)
• Probability of loss of alleles is greater in smaller populations
• When an allele frequency becomes 100%. The other alleles are lost by chance

  Fixation
• Fluctuations are much larger in smaller populations
• What is the probability of fixation of an allele if its starting frequency is 0.20, or 20%?

  0.20
• What is the probability of fixation of an allele if its starting frequency is 0.60 or 60%?

  0.60
• As populations get smaller, the probability of fixation or extinction of alleles go up
• In a large population, many more generations are required before the allele is eliminated or fixed
• Frequency of heterozygotes in a population (% of heterozygotes)

  Heterozygosity
• Often used as an estimate of genetic variation in a population

  heterozygosity