[Unequal genetic contributions of parents to offsprings and their optimal control]

Due to the joint effects of natural and artificial selection, the proportions of genetic materials originating from different parents may vary in the gene pool of offsprings, and this creates a problem of unequal genetic contributions of parents to offsprings. It is shown that unequal genetic contribution substantially affects the genetic gain via realized selection differential and effective population size, and brings error to the empirical prediction formulae of selection response: R = i.sigma P.h2. The aim of breeding should be to select the genetically superior individuals and then to make more genetic contributions of better parents to offspring gene pool. However, the latter aspect has been ignored in theoretical study as well as in certain breeding practice. To deal with the problem, a method which takes maximizing genetic advance as general objective and considers some breeding restrictions, is suggested to control the percentage of genetic contributions. A numerical example from egg-type chicken breeding is used to demonstrate the effects of optimal control of unequal genetic contributions. The result indicates that at the same level of effective population size, the realized selection response for different traits under the optimal pattern of unequal genetic contributions could be 34.27-216.57% higher than that under the actual unequal pattern.