Sometimes, there might be two ova in the female's fallopian tube. When both of these ova are fertilized, two fetuses can begin to develop in the uterus at the same time. In this case, the twins are called dizygotic ('non-identical') or 'fraternal'.

Twins can also develop from one zygote, which divides into two embryos. These twins are called monozygotic ('identical'), meaning that they develop from one zygote, which splits and forms two embryos, Children have exactly the same genome and are called identical twins (twins with the same egg).


Dizygotic twins and monozygotic or identical twins.