Identical twins are formed when a single egg cell is fertilized by a single sperm cell, and the resulting embryo divides into two halves. Conversely, with non-identical or fraternal twins, two eggs are fertilized by two sperm, thereby creating two genetically unique fetuses that will not be more alike than siblings that are born at different times.
How many sperm fertilize an egg for identical twins?
By Andrea Rodrigo B.Sc., M.Sc. (embryologist).
Last Update: 02/23/2018
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics.