We all know there are two types of twins identical and fraternal.
Now scientists are adding a third category to the list., semi-identical twins.
Researchers say, semi-identical twins are more genetically alike than fraternal twins, but not genetically identical like identical twins.
Semi-identical twins are created when two different sperm cells fertilize a single egg, which then splits apart.
Doctors say cases of semi-identical twins exist, they just haven't been identified.