I have tried some research and found this thread here.
However the quote comes from 2005 and seems more en passante than stating facts.
Is there anything more factual and up to date? The most recent articles I can find are dated 2008.
I would hasten to add I know SFA about DNA.
Barring the rare but real possibility of a spontaneous mutation after geminization, yes, they do.
Remember that identical twins result from the splitting of a fertilize ovum into two distinct zygotes. The entire genetic complement: mat4rnal and paternal nuclear genes and maternal somatic (ex. mitochondrial) genes – are of identical composition.
They’re pretty much identical. There are some inevitable mutations which occur after the zygote splits, but they rarely amount to any significant phenotypic changes.
If you had nigh-unlimited resources, you could sequence the genomes of both identical twins and most likely you’d find a handful of mutations that distinguishes the two. Even with these mutations the twins would be something like 99.999999% identical.
Note, however, that this does NOT mean there can’t be real biologic differences between the twins: some genes may get turned on in one and not in the other (epigenetic changes) and environmental differences can have biologic effects: cerebral palsy, for example, is caused by oxygen deprivation. This is even more complicated because genetics often plays a role inthse things: two twins might have a genetic tendency towards, say, colon cancer, but only one actually develops it.
So does that mean that identical twins are less ‘identical’ than a clone would be?
Clones would be even more subject to epigenetic effects, since twins have close to identical conditions throughout gestation but a clone would have wildly different conditions than its adult progenitor.
I would imagine that clones would be subject to the similar infinetesimal differences that twins are. If the clones were conceived and gestated in a completely controlled laboratory environment but the twins were not, you could make a credible argument that the DNA of those clones would be more similar than that of the twins, but it wouldn’t be a terribly strong argument.
How could they have identical DNA but not identical fingerprints? Or do they?
Well except if you started looking at the immune system like B-Cells. (Plasma and memory cells from what I remember.) Those would be different.
Well clones could have different mitochondrial DNA of course. (I mean if you used SCNT and used egg cells from 2 different mothers when you were doing the cloning you could have different mitochondrial DNA.)
Identical twins are naturally occurring clones.
However, two clones off the original adult that were gestated in the same womb would be as much/as little identical as two naturally occurring clones gestated in the same womb.
While generation of fingerprints is genetic, the exact pattern of fingerprints are not. Think of a “fingerprint generator” analogous to a random number generator. Identical twins/clones get the exact same model of generator, but the exact output of those two (or more) generators is not the same.
(Just in case you’re wondering - yes, identical triplets have also occurred in humans. Theoretically, identical quads, quints, etc. could also occur, but are much less likely to do so.)
Yes, that is one way in which clones may be LESS identical than naturally occurring identical twins. That might be used for clones generated at different times. However, if you want to do a batch of them all at once it’s easier to get one fertilized zygote, then split the resulting ball of cells a few times, before the point at which the cells start differentiating, in order to get multiple individuals for a cloning event.
As I understand it, identical twins will have the same broad patterns of loops, whorls, etc. in their fingerprints, but the exact details will differ. In fact, before genetic testing, this was one way to tell whether a pair of twins were truly identical or just fraternal twins who happened to look a lot alike (I’ve certainly known siblings who can only be distinguished by which one is older).
This was actually the subject of a show I saw on the BBC.
They did studies of identical twins to find out just how alike they were genetically.
The thing to remember is that genes express themselves. That is they turn on and/or off at certain times. It’s non genetic factors that cause this.
The long shot was when 2 year old identical twins are tested they show virtually everything is identical. Then they tested identical twins at various ages, all the way to identical twins in their 80s.
The short of it is, the older the twins got the less number of genes they had in common.
That’s true. But it’s hard to believe that was what the question was asking. The popular discussion of cloning is always a single donor and single child.
There’s no reason you couldn’t make dozens of clones once the process is perfected but The Boys from Brazil aside, that’s a less-likely real-world scenario.
This is most simply answered by saying that monozygotic “identical” twins should have identical nuclear DNA with (usually minor) variations in the expression of it, and different mitochondrial DNA (since each twin from the same ovum would have only about half of the ovum’s mitochondria and typically not any mtDNA from the sperm). While almost all the mtDNA would be maternal, each mitochondrion has its own DNA.
There are many many fine points around this topic, easily researchable online. Among other things, DNA replication/recombination is not absolutely perfect for a variety of reasons.
Factors external to the DNA itself might result in more significantly different phenotypic expressions in some cases.
My youngest and oldest sisters are an example of that. If you look at [del]photos[/del] headshots of them similar ages, it’s difficult to tell which is which. of coruse, since their age difference is about twenty years, it’ll never be a real issue.
Thanks very much for the answers.
Chief Pedant, the topics are probably easily researchable online, but (in my case at least) I would need to know what I was looking for to start with.
Cheers
The link I mentioned in my post in the old thread is dead.
It had pointed out that the repertoire of antibodies possessed by identical twins is quite distinct for each. This comes about by the somatic (hyper) mutations of the cells of the immune system. Without this mechanism, all of us would have a fixed spectrum of antibodies and might well encounter a “foreign protein” for which we had no antibodies and were neither able to generate the new antibodies either. In any case, the antibody producing cells of identical twins are definitely not identical.
By the way, here’s an old editorial “debunking” the notion of strictly identical twins. Still worth looking at.
Internet archive to the rescue!
The formatting is screwed up, and it may take a bit (or even a refresh) to load, but the actual article is still there.