Because identical twins develop from a single fertilized egg, they have the same genome, the entire set of genetic material found in an organism. So, any differences between them, even in traits with a significant genetic component – say one develops heart disease and the other doesn’t – are due to their environments. This is known as epigenetics.
Genes in DNA are ‘expressed’ when they’re read and transcribed into RNA, which is then translated into proteins. It’s proteins that determine many of a cell’s characteristics and functions. Epigenetic changes can boost or silence the transcription of specific genes, ramping up or inhibiting associated protein production, but they don’t change the genome. These changes, which are reversible, can affect a person for their entire life and mediate a lifelong dialogue between genes and the environment.
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