Definitions
Identical twins are also called monozygotic (Mz),
which means one egg. Identical twins have
identical genes and are always of the same sex.
Dizygotic
Fraternal twins are called dizygotic (Dz), which
means two eggs. Fraternal twins share
approximately 25 percent of their genes. One-half
of fraternal twin pairs are boy-girl, one-quarter
are boy-boy, and one-quarter are girl-girl.
