How different can genetically identical twins get?

[Simon Bridge]

Articles like this one tend to lead to speculation about simulating the whole embryology etc so that you can tell what someone looked like starting from their genome.

I've been taking the position that a simulation capable of doing that is unlikely because DNA does not work like that - it is not so much a blue-print as a recipe ... and that is probably going a tad far.

However, I am hard pressed to support this idea, and the state of knowledge has certainly changed since I last looked at this (early 90's - where it was generally considered doubtful that you could sequence fossil, or just very old, DNA.)

Identical human DNA does lead to identical twins ... but they tend to share a womb as well. Would the genetically identical fetuses develop identically in different wombs?

How different can genetically identical twins get?

 

[Borek]

Identical human DNA does lead to identical twins

Does it?

I don't know, I am sincerely asking. But somehow I doubt they are perfect copies even at birth.

 

[Ryan_m_b]

An interesting question would be how epigenetically identical monozygotic twins are.

 

[Simon Bridge]

@Borek:
I have known three sets of identical twins ... two sets were very very identical and one were just uncannily identical. But they all grew up together. One of the "seriously you cannot tell them apart" pair hated being identical and took pains to look different and it was still hard. It was only resolved when one got caught in a barbed wire fence and ended up with one of those scars over the eye.

I got to be able to tell them apart by their body-language ... which would take a while.
Seriously, their own parents couldn't tell.

However - via skeptics networks, I have heard that identical twins need not be all that identical. There is a tendency to learn to be identical as kids, and studies have tended to select for very alike twins for subjects.

@Ryan - thanks for the terminology :) that reminds me:

I am (JIC there's a pedant reading this) not including differences obtained through misadventure or surgery.

In a way what I am really asking is "to what extent does your genome determine your appearance?" But I'm trying to be clever. I was hoping that some fertility clinic has implanted identical kids in different mothers and kept track. I doubt we'd get a deliberate experiment of this kind past the ethics committee.

 

[Simon Bridge]

Scientific American on twins not that identical.
http://www.scientificamerican.com/article.cfm?id=identical-twins-genes-are-not-identical

Stanford forum uses the "recipe" analogy:
http://genetics.thetech.org/ask/ask142