Genetics of Populations

What was one of the early criticisms of Mendel's work?

That Mendel studied discrete traits, while most observed traits in nature showed continuous variation.

How was the conflict between Mendelian genetics and continuous variation resolved?

By recognizing that multiple genes can contribute to a single trait, producing continuous variation.

What misunderstanding did Hardy clarify with his model?

That dominant alleles do not necessarily increase in frequency just because they are dominant.

What is brachydactyly and how did it relate to Mendelian inheritance criticism?

It's a dominant trait that didn't spread through populations as critics expected, highlighting population-level effects.

What are the two branches of genetics discussed in the presentation?

Transmission genetics and population genetics.

What are the key assumptions of the Hardy-Weinberg model?

No mutation, random mating, no natural selection, infinite population size, and no migration.

What does the equation p + q = 1 represent?

The total frequency of two alleles in a population.

What does the equation p² + 2pq + q² = 1 represent?

The expected genotype frequencies under Hardy-Weinberg equilibrium.

What type of equilibrium is genotype frequency under Hardy-Weinberg?

Stable equilibrium.

What type of equilibrium is allele frequency under Hardy-Weinberg?

Neutral equilibrium.

What does a selection coefficient s = 0 mean?

No fitness difference between genotypes.

What does a selection coefficient s = 0.5 indicate?

A 50% reduction in fitness compared to the most fit genotype.

In the pocket mouse example, which genotype was selected against in dark lava environments?

The light-colored homozygous genotype (A₂A₂).

What is directional selection?

Selection that consistently favors one allele over others.

What does it mean if allele A₁ becomes fixed in a population?

It reaches a frequency of 1.0 and all individuals carry it.

What is fixation?

The point at which one allele's frequency reaches 1 and others are lost.

What is overdominance?

When the heterozygote has greater fitness than either homozygote.

What is underdominance?

When the heterozygote has lower fitness than either homozygote.

What is frequency-dependent selection?

Fitness of a phenotype depends on how common it is in the population.

What kind of equilibrium results from overdominance?

Stable equilibrium that maintains both alleles in the population.

What is the mutation-selection balance?

An equilibrium between new mutations and natural selection removing them.

What is the equation for mutation equilibrium frequency p*?

p* = n / (m + n)

If mutation from A₁ to A₂ occurs twice as often as the reverse, what is the equilibrium frequency of A₁?

1/3

What kind of mutations are typically removed by selection?

Deleterious mutations.

How can a harmful allele persist in a population?

Through balancing forces like overdominance or high mutation rate.

What is assortative mating?

Individuals preferentially mate with others that are phenotypically similar.

What is disassortative mating?

Individuals mate with those that are phenotypically dissimilar.

What is inbreeding depression?

Reduced fitness due to increased expression of deleterious recessive alleles.

What does Wright's F-statistic measure?

The degree of inbreeding or genetic similarity within a population.

How does migration affect genetic variation?

It increases genetic similarity between populations but can oppose local adaptation.