Heterosis in Poultry

Abstract

TESTING programs to identify superior cross combinations are of importance in commercial poultry breeding. The value of a testcross program as an aid to genetic improvement depends on the degree of accuracy of the measure of performance. Performance of a strain or line in cross combinations may be evaluated in terms of general and specific combining ability. The latter were originally defined by Sprague and Tatum (1942), who utilized a diallel crossing system as the testing procedure. General combining ability may be defined as the average performance of a breed, strain or a line in hybrid (i.e. cross) combination. Specific combining ability may be defined as the deviation in performance of a cross from that which would be expected on the basis of the average performance (general combining ability) of the parental breeds, strains or lines involved. According to these definitions and the genetic mechanisms involved, general combining ability is …