An XXY sex chromosome constitution in a house musk shrew (Suncus murinus L.) with testicular hypoplasia.

An adult male house muck shrew with an XXY sex chromosome constitution was found in a laboratory-bred colony. Maternal origin of the additional X chromosome was demonstrated. The external appearance of the animal was normal, but the testes were small and displayed a high density of interstitial cells. The seminiferous tubules were narrow and contained only Sertoli cells.