genetic drift Flashcards
What four major factors altern allele frequencies and bring amount most evolutionary change?
- mutation
- selection
- genetic drift
- gene flow
What is genetic drift?
- random changes in the frequencies of two or more alleles or genotypes within a population
- process of random fluctuation in allele frequencies due to sample effects in a finite population
Genetic drift has the most effects on ….
SMALL POPULATIONS
genetic drift tends to ______ genetic variation through _____ of alleles
REDUCE GENETIC VARIATION THROUGH LOSS OF ALLELES
What are 5 general features of genetic drift?
- GD is unbiased (frequencies can go up or down)
- fluctuations increase in small populations
- causes genetic variation to be lost
- causes populations to become difference
- alleles can become fixed without selection
Alleles with _____proportions are more likely to become ____
Alleles with higher proportions are more likely to become FIXED
what is an alleles probability of fixation?
- its original frequency!
New mutations are more likely to be _______in small populations than in large ones
New mutations are more likely to be FIXED in small populations than in large ones
What is coalescence?
- derivation of the gene copies in one or more populations from a single ancestral copy, viewed retrospectively
- as a result of coalescence, a populations will eventually become monomorphic for one alleles or the other, and that one allele will be fixed
What are some consequences of genetic drift?
- no allele is more fit than any other (drift is RANDOM with respect to fitness)
- some alleles will randomly increase their frequency in pops
- in finite pops, equally fit alleles are at risk of disappearing
Genetic drift is a function of…
POPULATION SIZE
What is effective population size?
- number of individuals in an ideal population where the rate of genetic drift is the same as in the actual population
- all real reproducing individuals
What is the bottleneck effect?
- sudden reduction in population size due to a change in environment
- the resulting gene poo; may no longer reflect the original populations gene pool
- if the population remains small, it may be further affected by genetic drift
what is inbreeding depression?
- reduction in fitness due to inbreeding and increase in homozygosity
What is the founder effect?
- when a few individuals become isolated from a larger population
- allele frequencies in the small founder population can be different from those in the larger parent population
- loss of genetic diversity
4 major points on genetic drift?
- GD is significant in small pops
- GD causes allele frequencies to change at random
- GD can lead to loss of genetic variation within pops
- GD can cause harmful alleles to become fixed
