Sex ratio and testis size in mice carrying Sxr and T(X;16)16H.

Mice heterozygous for the T(X;16)16H translocation and carrying Sxr on their normal (inactive) X chromosome (ie, T16H/X Sxr individuals) may develop as males, females, or hermaphrodites. The proportion of males varied from 22% to 65% depending on the source of the normal X chromosome. A model is proposed, according to which relatively small variations in the spreading of inactivation from the X chromosome into the attached Sxr fragment produce large changes in the proportion of males. Testis weight in T16H/X Sxr males was found to be significantly smaller than in X/X Sxr males, irrespective of the source of the normal X chromosome.