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.
T â¦ hese are the most common type of twins. With identical twins, it is the zygote that divides into two embryos, so you wouldn't say that the embryo divides. This usually occurs between 3-8 days after fertilization and the embryos will have one placenta and two amniotic sacs. Sometimes it will occur before this time and each will have a placenta and a sac.