When we are out, I always get asked if the girls are twins and that's almost always followed by whether or not they are identical. The following information comes from
here.
■Monozygotic (MZ) multiples (can be twins or higher-order multiples) were created when one fertilized egg split to form two or more embryos.
■Dizygotic (DZ) or trizygotic (TZ) multiples were created when two or more eggs were fertilized.
■Triplets and higher-order multiples can be any combinations of monozygotic and di/trizygotic.
Monozygotic multiples are commonly known as “identical” and di/tri/quadzygotic are known as “fraternal.” Some people assume that because 2 kids are "identical" that they are the same in every way. This is not true. When an egg splits, the two new eggs go down their own genetic path. The DNA can change in very simple ways. Besides that, there are internal and external conditions that make the two new individuals exactly that, Individuals.
Did you know:
■that monozygotic twins have more variation in birth weight than dizygotic twins, but by age 10 monozygotic twins are closer in weight and height than dizygotic twins?
■there are more sets of female monozygotic twins than male sets, and more sets of female conjoined twins than male sets?
■for most cancers, the risk of getting cancer isn’t any higher even if your twin has it
■even though monozygotic multiples aren’t supposed to run in families, there are some cases where it seems to recur in families or to occur more often than expected in families with dizygotic multiples
■language delays and learning disabilities seem to be more common among multiples
■dizygotic twins may run in families and may be passed down by both men and women (with men they can pass the trait to overovulate to their daughters)
■there are mirror image twins where some traits are opposites (one is left-handed and one is right-handed, one has hair that parts on the left and one on the right, etc)
We have never had the girls tested but the pathology report from their birth proves that they are identical.