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In high school they looked enough alike that they were able to switch places and fool the teachers. But despite all those similarities the brothers were always told they were fraternal, not identical twins.
“That was mom’s assertion,” said Greg. “The doctor told her that there were two placentas.”
That old assumption, and others, led a lot of twins and their parents to wrong conclusions about whether they were identical or fraternal twins. As many as one third of identical twins and all same-sex non-identical twins have separate placentas. And even when there are two placentas that might not be obvious to the delivering doctor.
It’s no wonder that correctly identifying twins as identical or fraternal is harder than you’d imagine. One recent study found that 32 percent of parents of identical twins were confused or plain wrong about whether their children were identical or not. About 29 percent of parents of fraternal twins had it wrong.
In hindsight it explains a lot for Greg and Alex. The two had always wondered if maybe the doctors had it wrong. Not long ago, Alex, a bioinformatician at Genentech with a Ph.D in biology, decided they should look at how similar they were genetically by testing with 23andMe.
“I thought there was a possibility that we might be semi-identical,” said Alex, referring to incredibly rare sets of twins. In those cases the twins are half fraternal and half identical having the same genes from one parent, but different genes from the other parent.
While there are plenty of important medical reasons for knowing whether twins are identical or not, there are also less concrete reasons that are no less important.
What the brothers found out from testing is that that they are indeed identical twins, not fraternal.
“The results were 100 percent shared DNA,” said Greg. “I said, ‘Wow, that’s not fraternal.’”
While the brothers said they can’t claim that their lives were changed by the news or did anything differently because of what they learned, both said the information was extremely valuable.
“The true essence of being a twin is to be identical,” Mike said. “Otherwise, you’re just siblings born at the same time.”
Tim Dang, a product manager here at 23andMe, and his brother Nick also grew up being told that they were fraternal twins, but learned about being identical twins after testing with 23andMe. Like the Convente twins and Alex and Greg, learning about being identical was an important detail for Tim and his brother.