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.
Now, for identical twins, these happen when a single egg is fertilized by a single sperm and it splits into identical halves-two babies with identical DNA are now formed. Identical twins are always the same sex and blood type. Identical twins are very similar in appearance.