A Genetic Hypothesis for Sex-Mating System Interactions in Growth of Cattle and Poultry

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Abstract
Heterosis in weaning weight of female Hereford calves was 15%; whereas it was 8% in males. Thus 50% of the heterosis in weight is associated with the extra sex chromosome. In turkeys, where the male is the homogametic sex, the heterosis in the male was 10% and 9% for linecrosses vs inbreds and crossbreds vs purebreds, respectively, and 3% and 1% in the females, or 70% to 80% of the heterosis was associated with the extra sex chromosome. In broilers, the heterosis in 10-week body weights was 14% for males and 8% for females. This corresponds to the turkey results. Thus in these species, as well, the greater heterosis is in the homogametic sex. It is suggested that this disproportional contribution to heterosis by the sex chromosomes be called homogametic heterosis. Males were heavier than females in cattle, chickens and turkeys, but the sex differences were small in linecross cattle; whereas they were large in hybrid turkeys and broilers. Maleness, per se, combined with homogametic heterosis seem to offer an explanation of these results.