Male, female and intersex development in mice of identical chromosome constitution.

In the preceding paper1, cytological evidence is presented to show that in ‘sex-reversed’ XX male mice2 the sex-reversing factor, Sxr, is carried on a dark-staining body located on the distal end of the paternal X chromosome. The X-chromosomal location of Sxr raises the possibility that it may be subject to the X chromosome inactivation process3. However, the regular segregation of Sxr and the absence of any indication that intersexes occur with a higher than normal frequency in Sxr stocks4 suggests that either inactivation of Sxr does not occur, or, if it does, that the proportion of cells with the Sxr-bearing X genetically active is sufficient to ensure normal testicular differentiation. Here we present information on the sexual development of chromosomally XX mice carrying Sxr in which the Sxr-bearing X chromosome is held in the inactive condition in most if not all somatic cells by use of the T(X; 16)16H (T16H) X-autosome translocated chromosome5–10 Mice of this genotype were found to develop as normal but sterile males, normal fertile females or intersexes.