AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

IMPORTANCE AND FEATURES OF HERITABILITY

Importance of heritability

• If the breeder chooses individuals to be parents according to their phenotypic values, his success in changing the characteristics of the population can be predicted only from knowledge of the degree of relationship between phenotypic values and breeding values. This degree of correspondence is measured by the heritability.
• Heritability in narrow sense is a measure of the strength of the relationship between phenotypic values and breeding values for a trait in a population.
• Heritability in the broad sense is a measure of the strength of the relationship between phenotypic values and genotypic values.

Features of Heritability

• Heritability is a population measure, not a value to be associated with an individual animal.
• Heritability is a property of the character and also of the population and the environment in which it is measured.
• The value of the heritability depends on the magnitude of all the components of variance (V_P = V_A+V_D+V_I+V_E), so change in any one of these will affect it.
• All the genetic components are influenced by gene frequencies and may therefore differ from one population to another. More variable environment reduces the heritability and more uniform condition increases. Therefore heritability of a trait is not fixed. It varies from population to population and from environment to environment.
• Heritability ranges from 0 to 1.
• If heritability is high, selection tends to be effective and vice versa.