BIOL 1020 Population Genetics

LECTURES 22-23

What is microevolution?

A change in allele frequencies in a population over generations

What 3 mechanisms cause allele frequency change?

Natural selection, genetic drift, gene flow

Of the 3 mechanisms that cause allele frequency change, which one consistently causes adaptive evolution?

Natural selection

What is a population?

A localized group of individuals capable of interbreeding and producing fertile offspring

What is a gene pool?

All of the alleles for all loci in a population

What does it mean when a locus is fixed?

All individuals in a population are homozygous for the same allele

There are 5 conditions for Hardy-Weinberg Equilibrium. The first is “No mutations.” If this condition does not hold (aka there IS a mutation), what is the consequence?

Gene pool is modified

There are 5 conditions for Hardy-Weinberg Equilibrium. The second is “Random mating.” If this condition does not hold (aka mating between close relatives), what is the consequence?

Random mixing of gametes does not occur, changing genotypic frequencies

There are 5 conditions for Hardy-Weinberg Equilibrium. The third is “No natural selection.” If this condition does not hold (aka natural selection occurs), what is the consequence?

Allele frequencies change when different individuals (genotypically) show consistent differences in survival/reproductive success

There are 5 conditions for Hardy-Weinberg Equilibrium. The fourth is “Extremely large population size.” If this condition does not hold (aka population is small), what is the consequence?

Allele frequencies fluctuate by chance over time (genetic drift)

There are 5 conditions for Hardy-Weinberg Equilibrium. The fifth is “No gene flow.” If this condition does not hold (aka alleles move between populations), what is the consequence?

Allele frequencies are altered

In genetic drift, does the chance of random deviation become greater in a smaller or larger sample?

Smaller sample

What does genetic drift describe?

How allele frequencies fluctuate unpredictably from one generation to the next

What is the effect of genetic drift on genetic variation?

It reduces it through losses of alleles

What is the founder effect?

When a few individuals become isolated from a larger population

What is the bottleneck effect?

A sudden reduction in population size due to a change in the environment (e.g. natural disaster eliminating a large chunk of a population)

Genetic drift is significant in small or large populations?

Small populations

What does gene flow consist of?

Movement of alleles among populations

When does heterozygote advantage occur?

When heterozygotes have a higher fitness (how well one can survive/reproduce) than do both homozygotes

What is a common example of heterozygote advantage?

The sickle-cell allele that causes mutations in hemoglobin also confers malaria resistance.

Selection favours individuals that are heterozygous for the sickle-cell allele