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.
When the young embryo splits, each half takes the exact same DNA, so identical twins have exactly the same genetic makeup. The making of Identical Twins. 1  A sperm and egg come together to share their genetic information and create a new human being.  The cells inside the egg divide and mulitply.