No, it doesn't. A small proportion, probably fewer than 10%-of dichorionic diamniotic twins are derived from one embryo. They would of course have to be the same sex. These twins are therefore monozygotic, from one embryo that split very early on-so each twin has its own placenta and membranes.
| Identical Twins
If an egg is fertilized by one sperm and then splits into two, the two embryos that are produced are always the same sex and are identical because they contain the same genetic material; these twins are known as monozygotic. | )
| Fraternal Twins
Fraternal (dizygotic) twins are the result of two separate eggs being fertilized by two sperms at the same time, so that two embryos implant and develop with two placentas. The twins may look different and be different sexes. | )
 |
Register to be entered into our weekly prize draw!