As a mother of identical twins I find THIS (click for link) fascinating.
Identical twins develop from a single fertilized egg, so they have an identical genome.But differences in their genomes can occur throughout their lifetime. Genes can be turned on or off, a process called expression, as the result of environmental factors like diet, exposure to toxins, stress, and exercise. So identical twins can be formed into biologically different people as the result of their life experiences and lifestyle choices. Which is a great example of the fact that we are all the product of both our biology and our environment. Our lives make us who we are.