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Identical Twins Not Identical After All

Posted by samzenpus on from the one-of-these-things-is-not-like-the-other dept.

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.""

5 of 159 comments (clear)

  1. Disease gene hunting by reprint · · Score: 3, Insightful

    This is certainly another tool for those hunting genes associated with disease. These are complex diseases however with multiple genetic alterations so the identification of a single gene may not provide the whole story. Also a gene identified this way may not apply to the larger afflicted populaton since this is a correlation seen in a small study group. It should be relatively easy to check though.

  2. Re:Wonder how this affects... by JeffL · · Score: 5, Insightful

    It doesn't have too much effect, really. MZ twins are similar on a trait because of genes that they share (traditionally, all of them) and environment they share (growing up in the same house, etc.) They are different on a trait due to environmental factors they don't share (such as going to different colleges) and error (measurement error in assessing the trait, random noise, etc.)

    DZ (fraternal) twins are similar on a trait due to the genes they share (on average, 50%, same as any other full siblings) and the environment they share. They are different on a trait due to the genes they don't share (on average 50%), environment they don't share, and error.

    These results say that the assumption that MZ twins share 100% of their genes is wrong. The real question is how wrong? Do MZ twins share 99.99% of their genes? Is that 0.01% difference right in the middle of some gene that has a large effect on the trait you're studying? For most of these new discoveries, it doesn't make any difference at all. Differences in silent mutations between twins isn't going to change scientists' conclusions that height is highly heritable (meaning: most of the difference in height between two people is due to the fact that they have different genes).

  3. Copying introduces errors by tsa · · Score: 3, Insightful

    When 3 billion basepairs are copied when a cell is divided, it seems logical to me that errors occur. So why isn't the fact that 'identical' twins are not truly identical a no-brainer to the experts? I know this remark sounds like a troll, but I'm genuinely surprised.

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    1. Re:Copying introduces errors by mrbluze · · Score: 3, Insightful

      Scientific research is only as good as the people conducting it and what motivates them. From what I've seen, only a small number of people are genuinely excited by the stuff they are researching. The rest of them are chasing a PhD or some other claim to fame. But also coming up with a good study and designing it well to make it valid is not easy. It takes creative imagination and intelligence. Whilst there are many people with these qualities, it's frighteningly hard to find them at scientific meetings.

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      Do it yourself, because no one else will do it yourself. [beta blockade 10-17 Feb]
  4. Re:Wonder how this affects... by Eivind · · Score: 4, Insightful

    Actually, scientists aren't (universally) that dumb.

    If identical twins are much MORE similar in intelligence compared to non-identical twins, we can conclude that there is a high likelihood that the difference is genetic.

    Identical twins should not normally have more similar nutrition (in pregnancy or thereafter) than nonidentical ones.