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.
Fraternal twins occur when more than one egg is fertilized. Normally, one egg is released from the ovaries each month, but sometimes there is more than one. Some women release multiple eggs in every cycle, a condition called hyperovulation. Women who hyperovulate are more likely to have fraternal twins.