Identical Twins Not Identical After All 159
Hugh Pickens writes "Contrary to previous beliefs, identical twins are not genetically identical. Researchers studied 19 pairs of monozygotic, or identical, twins and found differences in copy number variation in DNA which occurs when a set of coding letters in DNA are missing, or when extra copies of segments of DNA are produced. In most cases, variation in the number of copies likely has no impact on health or development but in others, it may be one factor in the likelihood of developing a disease (pdf). "Those differences may point the way to better understanding of genetic diseases when we study so-called discordant monozygotic twins....a pair of twins where one twin has a disorder and the other does not," says Carl Bruder, Ph.D. "If twin A develops Parkinson's and twin B does not, the region of their genome where they show differences is a target for further investigation to discover the basic genetic underpinnings of the disease.""
Re:Err..... (Score:4, Informative)
While it may seem obvious to the uneducated that twins are "different", there is a lot of research that shows high correlation, even when the twins are raised apart, so identifying the cause(s) of the differences and whether those are "nature" or "nurture" is still of value. Even within a family, the differences may be simply something like feeding order, where the earlier fed may get different (not necessarily better or worse) nutrition or bonding experience than the later fed, rather than, necessarily, a genetic difference.
When it is copy numbers, or very small polymorphisms, and there is some somatic variation, we can use the data to more closely identify which genetic values are associated with the variation.
That was known for quite a while (Score:5, Informative)
Re:That was known for quite a while (Score:3, Informative)
Also remember that many of your cells carry DNA of all those viruses you got exposed to without even noticing. And while we talk about infections, the immune system comes in mind, with all those crazy DNA recombinations taking place during its development. Not to mention spontaneous mutations which are not that insignificant tumorigenesis [wikipedia.org].
Nobody actually ever believed that twins are 100% identical. They just want to make up their story. Nothing new to see here
Re:Wonder how this affects... (Score:3, Informative)
I'll tell you what I first thought when I read this:
I read in, I think it was a Steven Pinker book, about studies done on identical twins using the big five personality traits [wikipedia.org]. What he said was that on the big five, identical twins raised together were roughly 50% similar, and identical twins raised apart were... roughly 50% similar. So when it comes to nature/nurture on the big five, you get 50% genetics, maybe 1-2% environment, the rest comes from ?????.
As you say, those numbers are probably based on the assumption of the genetic code being exactly the same, so those numbers can't represent reality as we know it now. But I'll be interested to see how the numbers fall out after the variance in twins' sequences is factored in. I would guess that it's the explanation for some of the ????? above, but how much?
Re:Copying introduces errors (Score:1, Informative)
Thanks.
Re:I cannot believe it (Score:3, Informative)
Re:This may explain WHY there are "identical" twin (Score:1, Informative)
Eh, from an evolutionary perspective there's another, simpler advantage to producing offspring at twice the rate...
Re:Disease gene hunting (Score:2, Informative)
Re:They're not identical triplets (Score:2, Informative)
Okay well the Dalhmers may not be identical, but they are not the only twins featured in Playboy. I've seen differing breast sizes in other twins as well.
(Let's see - College Girls Special Edition, circa 1999, two hispanic twins. One has C size and the other has B size (approximately). I had figured one had eaten more fatty food, but maybe it's in the genes.)