Rhonda J. Pomerantz, MD is a practicing Dermatologist (Skin Specialist) in New York, NY. Dr. Pomerantz graduated from New York University School of Medicine in 1989 and has been in practice for 28 years. She completed a residency at Suny Health Science Center. Dr. Pomerantz also specializes in Internal Medicine.
Identical twins form when one egg has been fertilised by one sperm and the zygote splits into two. This happens at the very earliest stage of development, when the zygote is no more than a cluster of a few cells.
Quick Answer. Paternal and maternal twins, commonly known as fraternal and identical twins, are distinguished by the different ways the multiple pregnancy begins. Identical twins begin as a single zygote that splits into two or more developing embryos. Fraternal twins are usually the result of multiple eggs being present for fertilization.