Zappykins said:
Actually, it's not that simple for many people. It's like saying "you have blue or brown eyes." Well, yes, those are the genes, but there are also other modifiers that give people, green, hazel, lavender, grey, pink, and some are two colour and heterochromic - sometimes cause by chimerism where people can contain to completely separate DNA strains from different people are in one body. There are XXXY people, and other sorts of 'intersex' combinations. Some x's are incomplete - so they are sort of between and X and a Y. So when you study something as complex as DNA and even more complex human personality and sexuality - it's easy to see how some people end up somewhere in the middle of the spectrum.
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Not to mention the fact that human chimeras are a disconcertingly common thing. There have been cases where physical parents have failed paternerty tests because they turned out to be chimeric. It's often just parts of the body that exibit the chimerism, but if that part is your sex organs, it's possible to have children that are genetically not yours.
This does not stop at same sex chimerism either, there is lots of intersex ones. There was a female athlete that got genetic testing done (because people alledged that she was a man in disguise or a transgender, possibly a hermaphrodite) and when they tested her hair they found two distinct sets of genetic material. One male, one female. She was an intersex chimera and it exibited in her hair. It is defently not as simple as: You either have one, or the other on a genetic level.
General rule of thumb, if someone has two diffrent hair- or eyecolors he or she probably has chimerism. (I have a friend that has three driffrent beard colors, red, blonde, and black, that I strongly suspect might be cause by this. In his case the three colors are evenly distributed, so his beard just looks red from further away.)
This of course has rather troubling implications for genetic testing for forensic purposes and crime prosecution. Some DNA samples might never be matched up with anyone even if the right person is tested, because the person in question might carry diffrent sets of DNA in diffrent parts of their body. Chimerism takes pretty extensive testing to detect, too.
