Two mice. One weighs 20 grams and has brown fur. The other is a hefty 60 grams with yellow fur and is prone to diabetes and cancer. They’re identical twins, with identical DNA

So what accounts for the differences?

It turns out that their varying traits are controlled by a mediator between nature and nurture known as epigenetics. A group of molecules that sit atop our DNA, the epigenome (which means “above the genome”) tells genes when to turn on and off. Duke University’s Randy Jirtle made one of the mice brown and one yellow by altering their epigenetics in utero through diet. The mother of the brown, thin mouse was given a dietary supplement of folic acid, vitamin B12 and other nutrients while pregnant, and the mother of the obese mouse was not. (Though the mice had different mothers, they’re genetically identical as a result of inbreeding.) The supplement “turned off” the agouti gene, which gives mice yellow coats and insatiable appetite

via Epigenetics research takes aim at cancer, Alzheimer’s, autism, other illnesses – washingtonpost.com.