Ethnic differences in testis size: a possible link with the cytogenetics of true hermaphroditism.

Data on human testis size, although scanty and suffering from lack of standardization, suggest the existence of marked ethnic differences, testes being larger in Caucasian than in Oriental populations. According to the cytogenetic evidence, the most frequent sex chromosome constitution found in Caucasian and African black true hermaphrodites is XX, while XY hermaphroditism seems to be more prevalent in Japan. Based on genetic data on testis size in mice, on embryological findings on the timing of gonadal differentiation in the gonads of XX and XY mammalian fetuses, as well as on a recent model of the genetics of gonadal differentiation, it is postulated that genes for large testis size predispose to XX hermaphroditism and those for small testis size to XY hermaphroditism.