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.
1 Identical twins share the same DNA-but do not have identical DNA. 2  When the egg splits into two halves to form identical twins, the DNA may not divide equally between the two cells. 3  The basic concept is similar to when you cut an apple in half, the two halves may not look the same.