Influence of B Locus Blood Groups on Adult Mortality and Egg Production in the White Leghorn Chicken

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The influence of the B locus blood group on adult viability and egg production was studied in two White Leghorn populations (S1 and S2) synthesized from inbred line crosses. Each line segregated for four B alleles. Four homozygotes and six heterozygotes were produced in each line over a five-year period, and for an additional three years tests on certain blood-group combinations were continued. A total of 4371 birds were included in the study. Greatest differences in blood groups were found in the S1 line, with the B2 and B21 alleles seemingly having favorable effects and with B1 having unfavorable effects. The B1 homozygote was consistently the lowest in egg production (53.2%) and highest adult mortality (40.4%). The relative spread in standard deviation units between the B1 and B2 homozygotes was more than three times greater in adult mortality than in egg production; B2 was incompletely dominant to B1. Within the S1 line, the superiority of the heterozygotes was mainly a consequence of the poor fitness of the B1 homozygote, suggesting that in a random-mated population B1 would be maintained only by mutation and not by a polymorphic mechanism.—Over the eight years of the experiment, adult viability of the B1 homozygote improved 4.4% per year (P<0.05). Assuming this regression results from natural selection, either of two hypotheses can account for the results: (1) The B locus is pleiotropic with natural selection for many B modifiers, and (2) the B locus is neutral but linked to a major fitness locus.

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