Time Trends in Estimates of Genetic Parameters in a Population of Chickens Subjected to Multiple Objective Selection

Abstract

EVIDENCE of changes in the genetic variation of populations under selection, as manifested by changes in heritability estimates, is present in the positive trends reported by Scosseroli (1957) and the negative trends reported by Yamada, Bohren and Crittenden (1958). Fairly constant estimates of heritability over generations in selected populations have been reported by Lerner and Dempster (1951), Dempster, Lerner and Lowry (1952) and Falconer (1955). Changes in genetic variance due to selection appear to be conditioned by the specific genetic constitution of the population at the commencement of selection. In fact, the developments of Lush (1948) show that genetic variance is maximum in the case of only two alleles when gene frequency equals .5 and hence average initial frequency of genes being selected could have an influence on trends in heritability estimates. Investigations pertaining to the effects of selection on genetic correlations are very limited. No significant changes in genetic …