Identical twins, by definition, should have the very same DNA. While the genome is virtually identical, says a report in the American Journal of Human Genetics, there are tiny and fairly common differences in the genetic makeup of twins.
Each set of twins involved in the study had the same DNA, but “evinced differences in the number of copies of individual DNA segments.” So some twins could have multiple copies of a segment of DNA, while their siblings might be missing the same segment altogether.
The study complicates our view of genetics, but might lead to a better understanding of why identical twins sometimes have significant differences in health. Parkinson’s disease, for instance, can develop in one twin and not the other, and until now environmental factors were thought to be the only explanation for that sort of thing.
What’s most remarkable about the study, to me at least, is that these geneticists claim to have discovered something that I learned from watching a video when I was seven. I am, of course, referring to the 1988 documentary Twins. The film follows two separated-at-birth twins, within whom a keen observer can detect subtle discrepancies in morphological phenotypes. One of the brothers, Julius, looks strikingly like a younger version of California’s governor, while the other brother, Vincent, looks a little more like some kind of goblin, possibly a gnome. Also, Vincent has latent criminal tendencies, and Julius is cursed with deeply sub-average intelligence. So while this study sheds a certain amount of light on the subjects of the film, I’m not sure that the scientists should go around talking about “original research.” At the very least, I hope that Ivan Reitman is credited in their bibliography.