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.
Multiple eggs are released or there is more than one ovulation. Both (or more) eggs are fertilized and this is how fraternal twins are made. This can happen with or without fertility drugs. One egg is released but splits in two. This is how identical twins are made. This can happen with or without fertility drugs.