Final answer:
Identical twins result from a fertilized egg dividing and then separating into two cells, originating from the same zygote and sharing identical genetic material. Fraternal twins are the product of two separate eggs fertilized by two different sperm, resulting in genetic distinctness akin to regular siblings.
Step-by-step explanation:
When a fertilized egg divides once and then separates into two cells, the result is the formation of monozygotic or identical twins. This is in contrast to fraternal twins, which develop from two different eggs fertilized by two different sperm cells. Identical twins are much more identical than siblings born at different times because they arise from the same zygote and have exactly the same genetic material.
Mitosis is the process of cell division that results in two genetically identical cells from the parent cell, and this is the process that occurs after a zygote is formed. Fraternal twins, or dizygotic twins, on the other hand, involve the fertilization of two separate eggs during an ovulation cycle by two separate sperm cells, resulting in embryos that are genetically distinct, similar to regular siblings.