Skinner – epigenetics and twins

Identical twins which have essentially the same genetics, when they’re very young and born they will look alike, they’ll have the same health and so forth. But when they get to be about teenagers or a little bit longer or certainly when they become adults, each one of the twins gets different environmental exposures. They may live in different places, they may have different diets, they have different exercise, their lifestyles will change a little bit. So over time then if you have 50 year old twins what’s known is that the diseases that the two twins get are generally different. That’s called discordant disease. The vast majority of identical twins do not have the same disease between the twins.  

If biology was totally dependent on just the DNA sequence then those twins should get the same diseases but that’s not what we see. So those environmental influences, those lifestyle changes, diet and everything else will slowly change the epigenetics around the DNA such that it changes what genes are on and off and the physiology of the different tissues so that eventually you’ll have a higher susceptibility for this twin to get maybe obesity and a higher susceptibility for this twin maybe getting arthritis when they get old enough. So essentially those discordant diseases is not due the DNA sequence but the environmentally changed epigenetics.