Â· 4 years ago. A mutation is a change in the genetic material of an organism. We are made from trillions of cells, each with a nucleus composed of DNA â a set of instructions that tells the cell what to do. Cells copy themselves with astonishing accuracy, but every now and then a piece of code is copied incorrectly.
Identical (or monozygotic) twins happen when a fertilized egg splits into two separate babies-usually within the first twelve days of Mom's pregnancy. After twelve days, the egg may not split entirely and result in conjoined twins.
Here are the different combinations: 1  Fraternal twins could be produced when eggs from one woman are fertilized by sperm from two different men. 2  A woman may carry twins conceived in-vitro with donor eggs, which could come from two different women. 3  Donor eggs from two different women could be fertilized by sperm from two different men. In this case, the twins may have no shared DNA unless the sperm and egg donors were related. They would be similar to step-siblings. A Word From Verywell. You are likely to have to answer the same questions about your twins repeatedly.