Re: "twin conjecture"

I think you mean "identical" twins. (Homozygous means that the two
sets of genes in one individual are the same.)

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

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

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