Epigenomes

As scientists discover more about the "epigenome," a layer of biochemical reactions that turns genes on and off, they're finding that it plays a big part in health and heredity...

The epigenome can change according to an individual's environment, and is passed from generation to generation. It's part of the reason why "identical" twins can be so different, and it's also why not only the children but the grandchildren of women who suffered malnutrition during pregnancy are likely to weigh less at birth.

"Now we're even talking about how to see if socioeconomic status has an impact on the epigenome," Szyf said.

The link is mine, but read more here.  Here is further explanation.