Identical Houses, Different Dimmer Settings

The 2005 study showed that young identical twins, in addition to having the same genes, have highly similar DNA methylation patterns. In contrast, the DNA methylation patterns in older twins diverge. The twins still have the same genes, but they are not activated in the same way. It’s like two identical houses but with dimmer switches set to different levels in every room. The variation in their gene activities can lead to physical and psychological differences sometimes observed in identical twins.