Confidence Intervals for Variance Ratios Specifying Genetic Heritability

Introduction. Phenotypic differences between individuals in most traits are partly due to differences in heredity and partly due to the differences in individuals' environments. Each developed trait is the result of the action of genes, the action of the environment, and the interaction of the genes and the environment. Heritability is a quantitative description of the amount of hereditary variation in a trait. It is important for the livestock breeder to know which traits have some degree of heritability if he wants to make any permanent improvement in his livestock. The only permanent changes in livestock quality are genetic changes brought about by a breeding program that will bring together favorable gene combinations. It is thus important for the breeder to be able to estimate heritability of a certain trait. One method of estimating heritability is by the technique of the analysis of variance. If r sires are each mated at random to s dams and t offspring result from each mating, the analysis of variance takes the form as outlined in Table 1, where Ca y 9b , and o-2 are respectively the variance components between sires, dams, and individuals. Using the variance components from Table 1, there are three ways of estimating heritability, h2: