Can Identical Twins Look Different?

Yes! Identical twins came from the same sperm and egg, so they have the same chromosomes and genes. But there are environmental differences that can affect the way they look and behave. For example, one twin may have been positioned in the womb in a way that she got more nutrients or blood supply and may be born larger than the other. The twins may have had different childhood illnesses as they grew up. They may have different lifestyles – exercise, smoking, drinking, nutrition, job stress, etc. As identical twins get older, they may look more and more different, because they are exposed to more diverse environments.

The science of epigenetics explains how these environmental influences can affect the genes. As a result of the environment, chemicals called “epigenetic marks” attach to the chromosomes and can turn specific genes on or off. So identical twins with identical DNA may have different genes turned on, causing them to look and act differently, and even to develop different diseases such as cancer.