Identical Twins...

[SlimeyLimey]

I'm lucky enough to have identical twin daughters, and found this article interesting. My girls are very much the same in many ways, and very different in others. As they have matured, their physical characteristics differ more than I had expected, although at birth one was 2.5 ounces and the other 3.4 ounces, so to some degree I assumed some variation in their physical growth.

At this point they're 15, and for the most part love good old mom and dad every day...except when we turn into those nagging parents that all kids love...

S

http://www.oregonlive.com/science/or...250.xml&coll=7

IS THAT TRUE?


Wednesday, March 19, 2008

The claim: Identical twins have identical DNA.
The facts: It's 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, although identical twins share very similar genes, identical they are not. The discovery opens a new understanding of why two people from the same embryo can differ in phenotype, as biologists refer to a person's physical manifestation.
The new findings appear in the March issue of The American Journal of Human Genetics. Scientists at the University of Alabama at Birmingham and universities in Sweden and the Netherlands examined the genes of 10 pairs of monozygotic, or identical, twins, including nine pairs in which one twin showed signs of dementia or Parkinson's disease and the other did not.
It has long been known that identical twins develop differences that result from environment. 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 such as diet and tobacco smoke -- have been implicated in the development of cancer and such behavioral traits as fearfulness and confidence, among other things.
"When we started this study, people were expecting that only epigenetics would differ greatly between twins," said Jan Dumanski, a professor of genetics at the University of Alabama at Birmingham who is an author of the study. "But what we found are changes on the genetic level, the DNA sequence itself."
John Witte, a professor of genetic epidemiology at the University of California at San Francisco, said the findings were part of a growing focus on genetic changes after the parents' template had been laid. This and other research shows "you've got a little bit more genetic variation than previously thought," Witte said.
In the meantime, a lot of biology textbooks may need updating.
The bottom line: Identical twins apparently do not have identical DNA.