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 »

Rarely, a boy and girl may be identical twins. This condition, called Turner Syndrome, afflicts very few pairs of twins. The gender difference occurs when an egg and a sperm pair that begins as two males, loses a copy of... 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 »

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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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 »

It might sound like a wayward twist from a movie, but it is possible for fraternal (not identical) twins to come from two different dads. The circumstances must be very specific, but some experts estimate that 1-2 percen... More »

Rarely, a boy and girl may be identical twins. This condition, called Turner Syndrome, afflicts very few pairs of twins. The gender difference occurs when an egg and a sperm pair that begins as two males, loses a copy of... More »