Expressivity of the Manx gene in cats.

New genetic data are presented which indicate that the assortment data for the mutant Manx gene, M, does not depart from normal expectation and does not enjoy a selective advantage at some stage of gametogenesis, as has been hypothesized. The variable expression of Manx taillessness is a remarkable and consistent feature of the Manx syndrome, encompassing the posterior skeleton, neural organization, and growth of soft tissues. The expression is partly genetic in origin, and the heritability is estimated to be in the region of h2 = 0.40 +/- 0.11.