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.
They are automatically the same genders, and they share the same placenta. Depending on when the egg (zygote) splits, they may share an amniotic sac, or they may each have their own personal space and membranes. 3. Semi-identical Twins. Semi-identical twins is when an egg splits and it is fertilized by two sperms! This type of twins share about 75% of their genotypes (50% from mother and 25% from dad). In theory, they will be more similar in appearance but they are not completely monozygotic. This kind of twins are name body polar twins.