Evidence suggesting the existence of two H-Y antigens in the mouse

An exceptional (C57BL/6 × BALB/c)F₁ male mouse, from an X-irradiated father, and lacking the H-Y (male) antigen, on the basis of skin-graft testing, was found. Conventional serological tests for H-Y antigen, however, were positive. His karyotype contained only 39 chromosomes, the Y chromosome apparently being absent. Although the testes were small, lacked germ cells, and were essentially Leydig cell tumors, the mutant was normal with respect to external male phenotype, accessory glands, and sexual behavior. The data suggest that the histogenic and serological tests for H-Y antigen may detect two different antigens, paralleling findings with mutants of theH-2 complex, where histoincompatibility can be generated without accompanying serological changes.