Blackwell Publishing

Quantitative genetics - What exactly is heritability?



The similarity between relatives in general, and between parents and offspring in particular, is governed by the additive genetic variance of the character. Many of the properties of an individual phenotype are accidentally acquired characters, such as cuts, scrapes, and wounds; if we measure these in parent and offspring they will show no correlation. V(A) = 0 for them.

Some characters, such as the number of legs per individual in a natural population of, say, red deer (pictured opposite), show practically no variation of any sort and for them V A trivially is zero. Additive variance is therefore often discussed as a fraction of total phenotypic variance: and it is this fraction that is called the heritability of a character

Heritability h2 = V(A)/V(P)

Heritability is a number between 0 and 1. If heritability is one, all the variance of the character is genetic and additive. Given that

V(P) = V(E) + V(A) + V(D) + V(I)

all the terms on the right other than V(A) must then be zero. Insofar as the factors other than additive variance account for the variance of a character, heritability is less than one.

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