Genetics of Quantitative Traits: Heritability, Selection, and Variance

What is a polygenic trait?

A trait influenced by many genetic loci.

What does phenotypic plasticity refer to?

The ability of a single genotype to produce different phenotypes depending on the environment.

What is quantitative genetics?

The study of the genetic mechanisms and evolution of continuous phenotypic traits.

How does the Hardy-Weinberg principle relate to polygenic traits?

It can be extended to understand the genetic variation in polygenic traits.

What is broad sense heritability (H2)?

The proportion of total phenotypic variation of a trait attributable to genetic differences among individuals.

What does narrow sense heritability measure?

The proportion of phenotypic variance explained by the additive effects of alleles.

What is the equation for estimating evolutionary response to selection?

R = h2 x S, where R is the evolutionary response, h2 is heritability, and S is the selection differential.

What is the selection differential (S)?

The difference in the mean of a trait in reproducing individuals and the mean of the trait for the general population.

What are the three modes of selection on quantitative traits?

Directional, stabilizing, and disruptive selection.

What is linkage equilibrium?

It exists if the occurrence of an allele at one locus is independent of the presence or absence of an allele at a second locus.

What is linkage disequilibrium?

It exists if the occurrence of an allele at one locus is nonrandomly associated with the presence or absence of an allele at a second locus.

What is a supergene?

A group of functionally related genes close enough together to segregate as a unit.

What is a quantitative trait locus (QTL)?

A section of DNA that correlates with variation in a phenotype.

What is the significance of QTL analysis?

It links traits with genes and helps identify genes contributing to variation in traits.

What is phenotypic plasticity in snowshoe hares?

The ability of snowshoe hares to exhibit different phenotypes based on environmental conditions.

What does the reaction norm predict?

It predicts how different genotypes respond to environmental changes.

What is the relationship between genetic variance and environmental variance?

When environmental factors play a bigger role, VE > VG; when negligible, VP ≈ VG.

What is the role of SNPs in genetics?

SNPs can be used as markers to detect the presence of disease-risk alleles.

How can plasticity evolve?

Differences in phenotypic plasticity may be heritable, allowing adaptive plasticity to evolve.

What does high heritability indicate about a trait?

It results in a larger evolutionary change in response to selection.

What is the significance of the slope in heritability estimation?

The slope represents the heritability of a trait.

What factors influence the evolutionary response (R)?

The strength of selection (selection differential, S) and heritability of the trait (h2).

What is the effect of additive components on phenotypic variance?

When components of variation are additive, genetic and environmental variance sum to total phenotypic variance.