It’s a phenomenon that baffles many twin researchers: Why do so many twins think they’re fraternal (DZ) when in fact they’re identical (MZ)?
For starters, many identical twins and their families are very in tune to their physical and social differences—however subtle—rather than their greater similarities. They believe that if one is more outgoing or an inch taller, for instance, this is proof enough to classify them as fraternal because…aren’t all identical twins identical?
Although MZ twins have the exact same DNA, there are differences in their epignome or the way that their genes are “organized” within a cell, accounting for variations in both their physical appearance and personality.
Zygosity misdiagnosis often begins with the medical community where many parents are given incorrect information regarding their twins’ zygosity either during a routine ultrasound during the pregnancy or at the birth. Why is that? Many technicians and obstetricians simply don’t know the physiology of twinning. Although a careful examination of the placenta is helpful it’s not one hundred percent accurate. Approximately 20 to 25 percent of identical twins can have separate placentas! On the other hand, two separate placentas from a set of fraternal twins can fuse together giving the appearance of one. It’s estimated that 55 percent of twin zygosity can be determined through the sex of the twins and placentation; the remaining 45 percent requires further DNA testing.
No wonder parents then carry the misdiagnosis into their homes where it’s perpetuated for years to come. It doesn’t help that at birth, identical twins can look vastly different. One twin can be significantly smaller due to a number of factors or their head shapes can be different from each other. So the incorrect zygosity makes sense to the whole family. Even as these twins age and they begin to look more alike, their zygosity is no longer questioned. It’s difficult to believe otherwise.
Furthermore, when you really think about it on a very basic level, it’s only natural for a twin, especially one who is older and aware of his own feelings, to believe that he is very different from a cotwin. As he grows into a young man and his quest for autonomy and individuality increases, it’s a normal reaction to think he is unique and different from all other human beings on the planet, even from his own cotwin.
The only true way of determing twin zygosity is through DNA testing. These days, home testing is not only reliable but relatively inexpensive running about $150. Many researchers believe that it’s vastly important for all twins to be tested at birth to determine their true zygosity.
How did you determine the zygosity of your twins?