What Is Epigenetics?

If one twin says doesn't have depression, then there's a 55% chance that the other one does. So if you have 100 identical twins in the population, 45 of them will both have major depressive disorder. And probably two are listeners. What about siblings, like fraternal twins? It's about 20% comments rate. All right. So it sounds like there's a large, large genetic component, but still a lot to be explained.