Gender is a whole lot more complicated than a lot of people think. Generally speaking, if one's missing a chromosome or has an extra, the results are catastrophic: children with trisomy 21 are not only intellectually delayed, but have a host of other medical problems. Those with trisomy 18 rarely live into their teens. And those are the chromosomal abnormalities that survive til birth. The rest are almost always miscarried early.
But mother nature plays weird games with our sex chromosomes all the time. People are walking around with XXY, XXX and XYY who are perfectly functional, although usually sterile. I've met a few women who were XO (Turner's syndrome). They look a little peculiar, but most have normal intelligence and can enjoy a normal life-span with treatment to prevent bone loss.
And then there are the cases where one's apparent gender (phenotype) is the opposite of what the genetic blue-print (genotype) indicates. Boys born with androgen insensitivity syndrome look like girls, and girls with adrenal virilizing syndrome are often mistaken for boys. I'm not even going into transgenders, where the person's brain belongs to the opposite sex.
Confining femininity to those "born women" is not only cruel, it's scientifically ignorant as well.
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