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Not So Identical

Apparently "identical" twins don't even have identical genetics:

Identical twins emerge when a zygote -- the fertilized egg that develops into an embryo -- splits into two embryos. As such, they should have the same genomes. The researchers speculate that as the cells making up each embryo divide over and over again during development in the womb, mistakes occur as dividing cells shuffle copies of their DNA into daughter cells.

But genetic differences between identical twins might also accumulate after development over a twin's life as well. "I think all our genomes are under constant change," Bruder told LiveScience.

I think that this has implications for cloning as well. It may not be possible to exactly clone an individual, and the differences could turn out to be quite noticeable.

[Update in the evening]

Per some comments, the key point in this story is that it has long been known that there are differences in twins (personality, eyesight, fingerprints, etc.). But those are things that can arise even from an identical genome. The genes are not a blueprint, but rather a recipe, and even if a recipe is followed carefully, the results are not always guaranteed to be the same. The point of the article is that, contrary to previous theories that obvious differences in twins could be attributed solely to different environments, that the genome itself wasn't necessarily the same. That is new.


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Jason Bontrager wrote:

Hmm, we'll have to come up with a new approach to creating identical duplicates then. Maybe scan the individual down to the atomic (or at least molecular) level and then construct the duplicate from the ground up with nano-machines?

Leland wrote:

I have identical twin daughters, and I was surprised to learn (several years ago) that they supposedly had the same DNA. They certainly have many differences that are easy to notice, once you spend time with them. They also have differences not necessarily noticeable. One is allergic to penicillin while the other needs glasses for a stigmatism. They are certainly not clones of one another.

Frank Glover wrote:

Recalling my early-seventies college days, during part of which, I worked in the Audio-Visual dept., I remember preparing to run a film for a class in the Criminal Science building (an episode from the CBS series 'The 21st Century).

Before I began, the (police uniformed) instructor made the point to his class that the film would assert that everyone has unique fingerprints, except identical twins, and that this was incorrect, even such twins will have different prints...

I've never explored the matter further (hey, I just ran the projector), but I must assume he spoke from real-world experience...

Edward Wright wrote:

the other needs glasses for a stigmatism.

Surely not.

astigmatism, astigmia - defect in an optical system in which light rays from a single point fail to converge in a single focal point

stigmatism - condition of an optical system (as a lens) in which light rays from a single point converge in a single focal point; normal eyesight

The American Heritage Dictionary of the English Language, Fourth Edition

sjv wrote:

They are certainly not clones of one another.

Actually, they are by definition clones of each other. It just is that "clone" does not mean "utterly identical", as the popular notion seems to be.

Mac wrote:

I have twins, a boy and a girl. I also have a gym membership with a kids room with people to watch them (full certifications and background checks). The girl I checked the kids in with last time saw that two of my children were the same age, and asked if my boy and girl were twins...I of course answered yes. She asked me them if they were identical. I asked her if she was truly qualified to watch my children.

Leland wrote:

Thank you Ed for noticing the space. I can count on you to ignore the forest for whatever tree catches your fancy.

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About this Entry

This page contains a single entry by Rand Simberg published on February 25, 2008 1:22 PM.

Creating An Appearance Of An Appearance was the previous entry in this blog.

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