Identical Twins Not Genetically Identical

Photo: Dave Banks/Flickr - via Geeks Are Sexy

You'd be forgiven to think that identical twins have the same DNA. After all, that's part of the plot of many crime novels and TV shows. Plus, "identical" means, well, identical. Right? Maybe not.

Turns out identical twins are actually not identical at the genetic level:

Even though identical twins supposedly share all of their DNA, they acquire hundreds of genetic changes early in development that could set them on different paths, according to new research.

The findings, presented Friday (Nov. 9) here at the American Society of Human Genetics meeting, may partly explain why one twin gets cancer while another stays healthy. The study also suggests that these genetic changes are surprisingly common.

"It's not as rare as people previously expected," said study presenter Rui Li, an epidemiologist at McGill University.

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