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Natural Science Forum / Biology / Microbiology / June 2005"twin conjecture"
Hi I once had a conversation with a friend studying biology. we were arguing how much does a person's DNA determine his/her appearance. I was arguing for 99%, while he was trying to tell me how small variation in environment can change proteins' regulation and so on and so forth about gene experession and phynotypes etc-- in short, he only knows that it's very complicated. After six month of studying, I have this question: how come twin looks so much alike? Was a person's appearance determined in the first few seconds of the person's existence? Because (I'm only guessing) after a few seconds, the environment for the two eggs (please substitute correct terms here) would be quite different? Maybe someone with a good microscope should look into this. Thanks > Hi > [quoted text clipped - 11 lines] > > Thanks Well, considering the 'eggs' share the same womb, they are pretty much in the same environment. So it's no surprise homozygous twins look the same. Even out of the womb, after most of the developmental steps which determine the differentiation of appearance have occurred, most twins still share the same environment. Granted they may not share the same room, but usually the same city, neighborhood, friends, sometimes girlfriends and boyfriends. A good microscope won't help you determine whether appearance is determined early. I would however go with your assessment that appearance is 99% genes. I would choose this because most wombs are very stable, predictable places. Normal humans are born every day far in excess of the proportion who suffered developmentally from an abnormal fetal environment. >> Hi >> [quoted text clipped - 15 lines] >in the same environment. So it's no surprise homozygous twins look the >same. I think you mean "identical" twins. (Homozygous means that the two sets of genes in one individual are the same.) >Even out of the womb, after most of the developmental steps which >determine the differentiation of appearance have occurred, most twins >still share the same environment. Granted they may not share the same >room, but usually the same city, neighborhood, friends, sometimes >girlfriends and boyfriends. An important aspect of twin studies is studying those who were separated at birth, and lived independent and different lives after that (and, usually, did not know each other). The number of such cases is surprisingly high, and they are of great research interest. There is a registry in the US for twins. I am not sure if it maintained by U Minnesota, though they are a leading center for twins research. Indeed it is not possible to separate effects due to generics per se and the environment before birth -- at least by traditional methods. We might note that with cloning technologies, this does become possible. Presumably over time we will be hearing some about this, for lab or farm animals. bob > I think you mean "identical" twins. (Homozygous means that the two > sets of genes in one individual are the same.) Indeed I meant monozygotic... it's funny how terms all swim in the same area of the brain. |
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