Mosaic character of spermatogenesis in carriers of the sex reversed factor in the mouse.

The "sex reversed" factor leads to development of XX male mice. It is inherited on one of the autosomes and transmitted through XY-Sxr carrier males. In the latter, spermatogenesis is studied under the aspect of gene dosis effects produced by the presence of the Sxr factor in addition to the Y chromosome. A mosaic pattern of normal and defective spermatogenesis is described. The defective areas are characterized by failure in late pachytene and metaphase I, and by appearance of spermatids with very large nuclei which degenerate in cap phase. The defects correspond to those observed in X0-Sxr spermatogenesis. Our interpretation is that in the normal areas only the Y chromosome, and in the defective areas the Sxr factor is expressed.