Gender.

Yes, but genotypes can produce different phenotypes. And there are plenty of X and Y chromosomal abnormalities out there. It remains murky.
Most are actually on the y chromosome. The x tends to carry more of the immune disorders, but I take your point.
 
Most are actually on the y chromosome. The x tends to carry more of the immune disorders, but I take your point.

I meant that chromosomal abnormalities can blur the lines of genetically determined binary gender - Fragile X, Kleinfelter’s, etc.
 
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