The probability of reactions among heterozygotes at the halothane locus was investigated in 6 generations of British Landrace selected for positive and negative reaction. Within lines the best fit was obtained with a complete recessive model in which no heterozygotes react. A proportion 0.20 of the expected heterozygous offspring from matings between the lines gave positive reactions, but this could mainly be explained by heterozygotes in the negative line. However, the incidence was higher when born out of positive compared with negative dams (0.28 y. 0.12, P<0.01), suggesting some form of maternal effect on the probability of reaction. When expected heterozygous females from positive and negative dams were backcrossed to positive males, there was no difference in incidence in the progeny (0.33 v 0.37), suggesting that the maternal effect was not inherited. It was concluded that although most of the observed reactions could be explained by a complete recessive model, the probability of a heterozygote reacting might be affected by maternal phenotype.

O. I Southwood, S. P Simpson, A. J Webb

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XI. Genetics of reproduction, lactation, growth, adaptation, disease, and parasite resistance., , 401–406, 1986
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