哺乳动物性别根据有或无Y染色体决定。Y染色体上基因诱导未分化性腺成睾丸。导致睾丸决定的基因称为“睾丸决定因子”(TDF),其生化性质不知道,但已被定位于人类Y染色体的短臂。无Y染色体时偶然也发生睾丸。“XX男性”睾丸小,其它表型接近正常,不育,其睾丸分化因基因组中有TDF而可能发生。为解释XX男性的Xg的异常遗传和TDF的获得,有人提示异常X-Y交换在其父减数分裂时就发生了。新近研究结果证实了X-Y交换假设。X- Sex of mammals is determined by the presence or absence of the Y chromosome. Genes on the Y chromosome induce undifferentiated glandular testis. The gene that leads to the testicle is called “testicle determinant” (TDF) and its biochemical properties are not known but have been mapped to the short arm of the human Y chromosome. Occasionally, testis occurs when there is no Y chromosome. “XX males” have small testes, other phenotypes are near normal, infertile, and testicular differentiation may occur due to TDF in the genome. To explain the aberrant inheritance of Xg and the acquisition of TDF in XX males, it was suggested that an abnormal X-Y exchange occurred at the time of her father’s meiosis. Recent findings confirm the X-Y exchange hypothesis. X-