Topic 2: Quantitative Genetics & Linkage (60 Q/A)

Define polygenic traits

A trait controlled by many genes, often with continuous variation.

Define additive genetic variance

The portion of genetic variance due to additive effects of alleles.

Define dominance variance

Variance due to interactions between alleles at the same locus.

Define epistatic variance

Variance due to interactions between alleles at different loci.

What is broad-sense heritability (H²)?

Proportion of total phenotypic variance due to genetic variance.

What is narrow-sense heritability (h²)

Proportion of phenotypic variance due to additive genetic variance.

What is the response to selection (R)?

Change in trait mean from one generation to the next due to selection.

State the breeder's equation.

R = h² × S

What is the selection differential (S)?

Difference between mean of selected parents and population mean.

What is recombination fraction (r)?

Probability of a crossover between two loci during meiosis.

Define linkage disequilibrium

Non-random association of alleles at different loci.

How does recombination affect gametic disequilibrium?

It breaks down disequilibrium over generations.

What is the effect of selfing on recombination?

Reduces effective recombination by decreasing heterozygotes.

What is the formula for effective recombination with selfing fraction S?

r_effective = r * (1 - S) / (2 - S)

Define D0 in gametic disequilibrium.

Initial disequilibrium coefficient of gametes.

How do you calculate expected gamete frequencies with no disequilibrium?

Multiply allele frequencies for independent loci.

Define coefficient of inbreeding (F).

Fractional reduction in heterozygosity relative to random mating.

How does inbreeding affect heterozygosity?

Decreases it, increases homozygosity.

How does outbreeding affect heterozygosity?

Increases heterozygosity, negative F.

Define inbreeding depression (δ)

Reduction in fitness due to homozygosity of deleterious alleles.

Give an example of positive assortative mating.

Mating between individuals with similar height.

Give an example of negative assortative mating

Mating between individuals with different MHC genotypes.

Define autozygous

Individual with two alleles identical by descent.

Define allozygous

Individual with two alleles not identical by descent.

Define self-fertilization (selfing)

Mating of an organism with itself.

What is the equilibrium inbreeding coefficient with selfing fraction S?

F_eq = S / (2 - S)