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.
Early splitting also means that the twins are perhaps less identical than those who separate at the late blastocyst stage. Around a quarter of all identical twins are said to be mirror images of each other. This means that the left side of one twin exactly matches the right side of the other.