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.
Twinning after 12 days post-fertilization will typically result in conjoined twins. 1  Dichorionic/Diamniotic : each twin has his/her own placenta, chorion and amniotic sac. 2  Monochorionic/Diamniotic: twins share placenta and chorionic sac but have their own amniotic sac. 3  Monoamniotic/Monochorionic : twins share placenta, chorionic and amniotic sac.