Heterosis and Selection in the Domestic Fowl

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Abstract
Hybrids, generated by crossing highly selected and mildly inbred strains from two distince breeds (viz. Australorp and White Leghorn) of Gallus domesticus, showed appreciable hybrid vigour with respect to the trait used in the parental lines as selection criterion, and also with respect to certain other traits. In the closed lines, bred from both hybrid, performance in egg-production traits showed a marked decline. As a result of subsequent conventional selection, different traits showed different response. Models for the types of gene action contributing to hybrid vigor are suggested. Some of the objections to the proposed models and the alternative models implied in such objections, are outlined. Further breeding experiments are tentatively suggested, with the intention of approaching a decision be tween these alternatives.