No, two men's sperm cannot fertilize the same egg simultaneously. While it's possible for two sperm to penetrate an egg (a condition called polyspermy), this usually results in a non-viable zygote. The resulting embryo typically won't develop normally due to an abnormal number of chromosomes. This is because a normal fertilized egg contains one set of chromosomes from the mother's egg and one set from the father's sperm. If two sperm fertilize the egg, there are three sets of chromosomes, leading to a triploid chromosome set, including three sex chromosomes. This results in faulty chromosome segregation during cell division, stopping development. [1, 3, 4, 8]
A related but distinct scenario is the rare occurrence of heteropaternal superfecundation, where two separate eggs released during the same ovulation cycle are fertilized by sperm from two different men. This leads to fraternal twins with different fathers. [6, 9, 10]
While reports of semi-identical twins, resulting from one egg being fertilized by two sperm from the same father, exist [2, 5, 7], this is an extremely rare exception. These cases are unique and not the same as two different men's sperm fertilizing a single egg. The genetic consequences of polyspermy typically prevent normal development.
- Key Points:
- Polyspermy (multiple sperm fertilizing one egg) usually leads to an unviable embryo.
- Heteropaternal superfecundation results in fraternal twins with different fathers but involves two separate eggs.
- Semi-identical twins are exceptionally rare and result from one egg and two sperm from the same father.
