But, for a woman in New Jersey suing for child support, things are a little more complicated. It turns out the man she thought was the father of her twins was only the father of one of the pair. Here are the different types of multiple births:. In this case, two different sperm impregnate two different eggs. This is what happened to the woman in New Jersey.
A New Kind of Twin - Science in the News
What increases the odds of having twins?
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Can Sex During Early Pregnancy Cause Twins? An OB-GYN Explains Away This Myth
There are two basic twin types now, identical and fraternal, but a third type is the focus of a new discovery. The story of these one-of-a-kind twins begins after natural conception and an uncomplicated term pregnancy, when the newborns were brought to the attention of science because one is anatomically male and one has sexually ambiguous genitalia. For the first time, researchers have identified twins that are identical on their mother's side, but share only half of their father's DNA. Lead investigator Dr. Vivienne Souter says that while the term semi-identical provides some idea of how the twinning occurred, it is "an oversimplification.
Sets of twins are commonly grouped into two classes: monozygotic, or identical; and dizygotic, or fraternal. Identical twins result from a fertilized egg an egg that has fused with a sperm cell dividing in two. Both newly identical fertilized eggs can then go onto to develop into their own organisms, sharing identical genes, the functional units of DNA.