Semi-Identical Twins Announced

Scientists Are Now Reporting that Twins Can Be Semi Identical

You have always heard that twins are either fraternal or identical, but scientists have now reported that twins can be what they call semi identical too. There have been twins that were discovered to be identical on their mom's side of the equation but only share half of their genes on their dad's side.

"Their similarity is somewhere between identical and fraternal twins," a geneticist, Vivienne Souter, of the Banner Good Samaritan Medical Center in Phoenix, Arizona said and added. "It makes me wonder whether the current classification of twins is an oversimplification."

There are 5 main combinations of twins. Identical twins that are both males and identical twins that are both females are two of the combinations. When one fertilized egg splits into two embryos identical twins are created. They are always the same sex and share the same placenta.

Fraternal twins make up the other three combinations of twins, a set of twins that are both female, a set of twins that are both males and a set of twins where one of them is a male and the other is a female. When two eggs are fertilized at the same time, each with a different sperm, the result is fraternal twins. They can be the same sex or opposite and they each have their own placenta.

Fraternal twins where one of the twins is a male and the other is a female is the most common result for twins, this combination makes up about 40% of all twins that are born.

A 6th combination that is extremely rear, estimated one in 200,000 births, that can occur in twins is when they are conjoined. This occurs when the zygote of identical twins fails to completely separate. Sadly about have of conjoined twin pregnancy end in stillbirths.

The semi identical kind of twin occurs when two sperm cells fertilized one egg, this is said to be also extremely rare, and then split into two embryos. No studies have been done that can provide statistics of how many twin births result in these kind of twins.