Nonidentical twins occur when a woman produces two separate eggs that are then fertilized by two different sperm cells. The resulting twins sometimes look alike, but have separate genetic identities, like children of the... More »

Identical twins develop from one fertilized egg that splits into two parts, while fraternal twins are born from two different eggs and sperm cells. In both cases, the twins share the same womb and are usually born within... More »

Because they come from the same egg, identical twins are always the same sex according to the National Health Service. Fraternal twins are from two separate eggs, which means that they can be different sexes. More »

Fraternal twins, also known as dizygotic twins, occur when two separate eggs are fertilized by two separate sperm. This results in two babies who are not identical and who do not come from the same egg. Fraternal twins c... More »

Dizygotic twins, also known as heterologous or fraternal twins, develop when two separate eggs are fertilized at the same time within the uterus. Dizygotic twins do not have identical genetics and can be of the same sex ... More »

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Artificial embryo twinning is a method of making clones that mimics the natural process of creating identical twins, according to the Genetic Science Learning Center. It uses the same approach as natural cloning, but it ... More »

The exact cause of Siamese twins, more accurately known as conjoined twins, is not entirely known. Since the prevalence of conjoined twins is thought to be higher in southeast Asian and African populations than in Caucas... More »