Posted on 03/15/2008 12:24:17 AM PDT by neverdem
Really?
THE FACTS
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 person’s 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 Parkinson’s 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 ...
“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 well—though I haven't checked!)
:)
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