Skip to comments.The Claim: Identical Twins Have Identical DNA (No, copy-number variation strikes again!)
Posted on 03/15/2008 12:24:17 AM PDT by neverdem
It is a basic tenet of human biology, taught in grade schools everywhere: Identical twins come from the same fertilized egg and, thus, share identical genetic profiles.
But according to new research, though identical twins share very similar genes, identical they are not. The discovery opens a new understanding of why two people who hail from the same embryo can differ in phenotype, as biologists refer to a persons physical manifestation.
The new findings appear in the March issue of The American Journal of Human Genetics, in a study conducted by scientists at the University of Alabama at Birmingham and universities in Sweden and the Netherlands. The scientists examined the genes of 10 pairs of monozygotic, or identical, twins, including 9 pairs in which one twin showed signs of dementia or Parkinsons disease and the other did not.
It has long been known that identical twins develop differences that result from environment. And in recent years, it has also been shown that some of their differences can spring from unique changes in what are known as epigenetic factors, the chemical markers that attach to genes and affect how they are expressed in some cases by slowing or shutting the genes off, and in others by increasing their output.
These epigenetic changes which accumulate over a lifetime and can arise from things like diet and tobacco smoke have been implicated in the development of cancer and behavioral traits like fearfulness and confidence, among other things. Epigenetic markers vary widely from one person to another, but identical twins were still considered genetically identical because epigenetics influence only the expression of a gene and not the underlying sequence of the gene itself.
When we started this study, people were expecting that only epigenetics would differ greatly between...,
(Excerpt) Read more at nytimes.com ...
Sending to my identical twins...don’t ever try to play a game of chance against them. ;)
Not surprised: twins have different fingerprints.
Epigenetics is going to be the next great field in medicine.
What the article says is the they DO have identical DNA, but that changes can develop soon after fertilization. Another case of the headline being written by an brain-deficient moron.
What happens, is every time the cells divide, there are changes occurring. In other words, the succeeding generation of cells is not quite identical to the original cell. It can certainly make for some interesting differences in characteristics of a set of monozygotic twins, while there are still a lot of similarities.
Great information, neverdem. Thanks for posting this!!
There is only a suggestion that this isn't the case (which is the case for some, and if all the cells in a twin are taken into account, not only the first one).
or is that fraternal twins?
So their DNA is the same.....but different.
“Monozygotic twin” sounds pretty cool...maybe that will replace the expression “identical twin.” Discordant monozygotic twins would be identical twins who fight a lot with each other.
Good point. And they sure do change into different beings as they grow older and things happen to them.
“A few years ago in Dunwich a half-witted girl bore illegitimate twins. One of them was almost human.
-—H. P. Lovecraft
Which brings up the thought that, if you think you see identical twins at a bar, you've probably had too much...
Epigenetics is one thing. Copy number variation is quite another. It includes a range in the number of copies of a gene, from deletion, i.e. the absense of the gene altogether, to multiple copies of the same gene to different versions of a gene that makes a different, but functionally similar, protein, e.g. pancreatic amylase and salivary amylase. Click on the keywords copynumbervariation, copynumbervariations and cnv. It's not just simple Mendelian genetics and epigenetics.
No, check the link in comment# 1 and the keywords copynumbervariation, copynumbervariations and cnv. In the case of twins, copy-number variation means that the twins can have zero to multiple copies of the same gene.
It's unrelated to the main theme underlying this thread, copy number variations, but since epigenetics was mentioned so often, I managed to come across this review article from a conference in 2005. It's fascinating, even if it may be already out of date.
Not surprised: twins have different fingerprints.
....and fingerprints are not the result of genes?
The article says, "identical, they are not". My recollection is that fingerprints aren't programmed like genes. They "just grow".
Monkeys have fingerprints, too, BTW. (And suspect they are not alike in monkey-twins as wellthough I haven't checked!)
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.