Topic 7: Quantitative Traits and Heritability

Discontinuous Variation Defined

Differences that allow organisms to be assigned to discrete, sharply distinguishable phenotypic changes

Additive Genes Defined

Multiple genes contribute to a single trait, with each gene adding its effect independently to the final phenotype. Can be assigned their own quantitative values that indicate the contribution of the trait

Major Genes Defined

Majority of phenotype determination

Modifer Genes Defined

Minority of phenotype determination

Multigene Hypothesis Defined

Alleles of each of the contributing genes obeyed the principles of segregation and independent assortment and had an additive effect in the production of phenotype variation

What is the formula for Phenotype Categories

2n+1

What does the n represent in the 2n+1 formula Phenotype Categories

Number of genes involved

Threshold Traits Defined

Most polygenic and multifactorial traits exhibit a continuous phenotypic distribution but some cannot be divided into distinct categories

Genetic Liability Defined

Some alleles can push phenotypes toward affected end

What is the formula for Phenotypic Variance (Vp)

Vp = Vg + Ve

Genetic Variance Defined

Proportion of phenotypic variance that is due to differences among genotype

What are the Pure Bred lines equal too when considering genetic variance?

0

Environmental Variance (Ve) Defined

Portion of phenotypic variance that is due to variability of the environment by the individual members of a population

What are the three different kinds of allelic effects

• Additive Variance (Va)

• Dominance Variance (Vd)

• Interactive Variance (Vi)

Additive Variance (Va) Defined

Additive effects of all alleles contributing to a trait. Heterozygotes have an intermediate phenotype

Dominance Variance (Vd) Defined

Dominance relations. Heterozygotes phenotypes is not exactly intermediate

Interactive Variance (Vi) Defined

Epistatic interactions between alleles of different genes that influence a quantitative phenotype

Heritability Defined

Measures proportion of phenotypic variation that is due to genetic variation that can change with selection and will differ between populations depending on the environment or genetic variation

What are the two measurements of Heritability

• Broad Sense Heritability (H²)

• Narrow Sense Heritability (h²)

Broad Sense Heritability (H²) Defined

Estimates the proportion of phenotypic variation that due to TOTAL genetic variation

Narrow Sense Heritability (h²) Defined

Proportion of phenotypic variation due to ADDITIVE genetic variation

What is the formula to Broad Sense Heritability (H²)

H² = Vg/Vp

What is the formula to Narrow Sense Heritability (h²)

h² = Va/Vp

Selection Differentials (s) Defined

Measures the difference between the population mean value for a trait value for the mating portion of a population

What is the formula to Selection Differentials (s)

(Avg of mating population) - (Avg of total population)

Response to Selection (R) Defined

Predicted phenotypic change

What is the formula to Response to Selection (R)

R = s(h²)