Why a dog always gives birth to a dog, never a cat? Classic genetics has given a satisfying answer to this big old question. This is because dogs inherited dog DNA (or the dog “genes”). However, classic genetics provides no answer when the same question is asked at a different level. A single “mother cell” (a fertilized egg) can give rise to all kinds of different cells, skin cells, kidney cells, neurons, blood cells…...In this case, all cells inherited the same DNA from the original egg. Why the cells become so different? “Epi”-genetics helps to answer this question
