Types of Gene Action in the Inheritance of Ten-Week Body Weight and Breast Angle in Broilers

THE degree of heritability of a trait is an indication of the additive genetic variance of that trait. Breeders generally assume that the hereditary variances observed in body weight and width of breast are due to genes with additive effects. Present conventional systems of breeding have been designed to utilize this type of variance. Based upon favorable results that breeders have attained by selecting for body weight at a given age and the magnitude of the heritability estimates calculated for body weight, it is evident that additive genetic variance plays an important part in the inheritance of body weight. Less evidence is available regarding breast angle. In addition to additive genetic variance, hereditary variance may be due to dominance variations and/or epistatic variations. In ordinary breeding practices, epistatic effects are broken up every generation and therefore do not contribute a great deal to permanent changes in a population, while gene …