Three generations of selection for high and low donor competences of splenomegaly in chickens1

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Abstract
Three generations of two‐way selection were conducted for the donor competence of graft‐versus‐host reaction. Selection was effective in changing the donor competence. The average realised heritability over three generations was determined to be 0.41 by measuring the difference between the high (H) and low (L) lines. Reciprocal crosses gave intermediate values compared with those for their respective line offspring. Changes of gene frequencies at the B blood group locus were examined. In the H line the frequency of B 11 allele increased and of B 9 decreased, as expected, after selection in each generation. In the L line, however, the expected change was observed only in the first two generations. The direction of change reversed in the latter two generations. Relationship between the B locus genotypes and the degree of splenomegaly was different according to the sex of donors. In male donors, the B 9 /B 11 induced larger spleen than the B 9 /B 9 did, but in females the B 9 /B 9 was generally larger than the B 9 /B 11 especially in the L line.