Gene number estimation when multiplicative genetic effects are assumed - growth in flour beetles and mice

Estimation of the number of segregating genes affecting a quantitative trait in populations initiated from a cross of two homozygous lines is considered. Experimental data, for the trait in question, is assumed available on total response to recurrent selection initiated in the F2 or F3 generation, the initial additive genetic variance and the heterosis exhibited in the F1 generation. Appropriate procedures when multiplicative genetic effects are assumed are developed and reasons for assuming multiplicative rather than additive effects are indicated. These procedures were employed to estimate the number of genes affecting pupa weight in a population of flour beetles and growth in a population of mice. Estimates were 50-60 percent smaller than those obtained using familiar estimation procedures appropriate when no epistasis is assumed. However, the estimated numbers (about 200 and 100 for pupa weight and mouse growth, respectively) were still rather large.