THE LA TIMES has an interesting article on human gender, following the brouhaha over concerns about the gender of the South African athlete, Caster Semenya.
For years, sports authorities considered only the sex chromosomes: If they are XX, the athlete is female, XY and he is male. Technicians would swab the athlete's mouth to remove some cells, look at the sex chromosomes and make a determination.
But at the 1996 Atlanta Olympics, eight female athletes were determined to have XY chromosomes and were booted from the Games. Further studies, however, showed that they were physiologically female even though their genes said they were male, and they were reinstated.
Another possibility that could account for a disconnect between genetics and appearance is mosaicism, in which the individual has more than one set of genes, in some cases, some cells could be XX and others XY. That occurs because of a faulty division at a very early stage in the embryo, or if two embryos fuse, and can produce a variety of mixed sexual signals.