Question

Why does narrow sense heritability provide a better estimate of a population’s response to selection for sexual organisms? Make sure to include additive, dominant, recessive and epistatic genetic variation in your answer.

Answer 1

Heritability is a measure of how much phenotypic variation in a population is due to genetic factors. Generally, a phenotype is affected by the genotype, environment and the interaction between the genotype and environment.

Ih=f heritability is high, it would mean that the phenotype is largely affected by the genotype with the environment having only a small impact on the phenotype.

Heritability is not the proportion of a phenotype that is genetic, but the proportion of phenotypic variance that is genetic.

Heriatbility is of two types -

Broad sense heritability (H²) = (Genotypic variance)/ (Phenotypic variance) or V_G/ V_^P

It reflects all possible phenotypic variance due to the genotype.

V_P = Environmental variance (V_E) + V_G + V_GE (interaction between environment and genotype)

V_G = V_A (Additive genotypic variance) + V_D (Dominance genotypic  variance) + V_I (Epistatic genotypic variance)

Narrow sense heritability (h²) = V_A/ V_P

It reflects all possible phenotypic variance that is due to additive genotypic variance alone.

Additive genotypic variance refers to the genetic effects wherein every allele of all the genes that encode for a particular trait has a small effect on the phenotype and the phenotype thus depends on the sum of all these allele with each allele contributing equally.

For estimating the response of a population to natural selection, narrow sense heritability is a better option because natural selection depends on additive gene effect and also that the resemblance in a population among the relatives is largely driven by additive genetic variance.