Ecology L7 Genetic drift

Genetic drift

Stochastic events that alter allele frequency; chance inheritance of single allele of heterozygous parent

As populations get smaller, ___

The risk of an allele leading to loss or fixation increases

5 features of genetic drift

1. Genetic drift is unbiased (allele is as likely to go to fixation as to loss)

2. Genetic drift causes genetic variation to decrease (less heterozygotes)

3. Random fluctuations in allele frequency are larger in smaller populations (effects of drift more severe in small populations)

4. Fluctuations in allele frequency are due to random sampling error, so each population will follow its own evolutionary path

5. Genetic drift can produce substantial changes is allele frequencies if given enough time

The likelihood of an allele going to fixation= its___ in the population

initial frequency

If allele A has an initial frequency of 0.6, what is the likelihood that the allele will go to fixation and loss?

60% chance to go to fixation, 40% chance to go to loss

Effective population size definition and equation

N_{e}=\frac{4N_{f}N_{m}}{N_{f}+N_{m}}

Equal to the number of individuals in an ideal population the produces the rate of genetic drift seen in the real population

Population bottlenecks

Situations in which a population is reduced to a small size for a number of generations, greatly decreasing the variation in alleles

Founder event

occurs when a new population is begun from a small number of individuals thus shifting the allele frequency away from the original population

Selection coefficient (s)

A calculation of the fitness increase of a beneficial allele

if s>1/Ne

The allele is under stronger selection than drift

If s<1/Ne

The allele is under more drift than selection