A seven-year-old girl with a Y chromosome is providing new clues about a possible “master switch” of maleness.
The girl has the normal chromosome count – 46 – and should be male. Other children who have the male sex chromosome but do not appear to be boys have been found to have gene mutations that temper the Y chromosome’s effects. However this child doesn’t have ambiguous gonads, shrivelled testes or other developmental defects. She instead has a normal vagina, cervix and set of ovaries.
The great and far-too-long-enduring myth about maleness and femaleness is that XY always equals boy and that XX always equals girl, and that karyotypes somehow infallibly predict sex. Hence, the existence of laws in the US that only XY men may marry XX women. There are many people who are neither.
Intersex people at least have known for some time that the XX and XY myth is simply not true. There are far more complex mechanisms at work. This article sheds some light on one of them.