“Boys have a penis, girls have a vagina.”
- Unnamed little boy, Kindergarten Cop
Our twins are pretty dang cute. When we’re in public a stranger often asks if they are twins. Which is cool. I mean, Gray’s noticeably taller and thicker than Ellie. Yep, they’re twins.
“Are they identical?” A third of the time that question follows. And then I lose my shit.
It’s a boy and a girl.
“Naw,” I passively answer as I move along, uninterested in correcting the ignorant stranger.
This happens enough to my wife and I that it’s time for some education. Grab a seat, pull out your notebook and let’s begin. There will be a quiz at the end of the lesson.
Zygotes and shit
A zygote is a fertilized female reproductive cell. Identical twins are monozygotic. That means the fetuses formed from one fertilized egg that contains either XY (male) or XX (female) sex chromosomes, and then that one egg splits into two. As a result, there are two males or two females that share the same DNA and have similar attributes.
When two separate eggs are fertilized by two different sperm they are dizygotic (two zygotes). Fraternal twins are dizygotic and the combination can result in male or female, since they’re two separate cells. It’s the same genetic connection as regular siblings. They might look a like, they might not.
Let’s Break It Down
Two girls – identical or fraternal
Two boys – identical or fraternal
Boy/girl – fraternal
We ended up with twins because I didn’t want to pay a shit-ton of money for in vitro to have it not work. So I decided, against my anxious wife’s wishes, to increase the odds by transferring two fertilized A+-rated embryos into my wife’s uterus. And it fucking worked. Two embryos = two zygotes = fraternal twins.
Pop Quiz, Hot Shot
Gray and Ellie are:
A) Identical twins
B) Fraternal twins
C) Super cute, OMG OMG OMG
D) Like the velociraptors from Jurassic Park.
Identical twins share the same DNA. They were formed from the same reproductive cell. Penises and vaginas don’t share the same DNA strands.
Correct answer to quiz is D) Like the Velociraptors from Jurassic Park.