Principles of Genetics and Breeding

11.1.5 Heritability

Heritability tells us to what extent the differences we observe in an animal performance are due to inheritance. What causes some traits to be more heritable than others?

• It measures the degree to which offspring resemble their parents in performance for a trait. Thus, the ability of an individual to transmit its phenotype to the next generation can be viewed as heritability.
• If a trait is highly heritable, animals with high performance themselves tend to produce high performing offspring, and animals with low performance tend to produce low performing offspring. On the other hand, if a trait is not very heritable, performance records of parents reveal little about progeny performance.
• Heritability is one of the most important properties of a quantitative character. It expresses the proportion of total variance that is attributable to average effects of genes. This determines the degree of resemblance between relatives with respect to a character.
• Heritability (h²) is used in the study of metric characters for prediction of performance of the progeny. It expresses the reliability of the phenotypic value as a guide to the breeding value. It is the degree of correspondence between the phenotypic value and the breeding value of the character. It is computed as the ratio of additive genetic variance and phenotypic variance.

h²=V_A/V_P

• In general, phenotypes with h²’s ≥ 0.25 can be improved efficiently by individual (mass) selection;
• when h²’s are ≤0.15, family selection is needed to improve a population.
• When h² is ≤ 0.10, family selection is often ineffective, although some gains can be made when inbreeding is combined with family selection.