In an effort to spread understanding so that maybe complete strangers will stop asking me silly questions, I'd like to teach all y'all just a few things about the genetics involved with twins.
Identical twins are the SAME gender. Boy/girl twins are fraternal (unless of course you want to get crazy technical and talk about near-identical twins, but that's for Genetics 201 and we don't want to get ahead of ourselves).
Identical twins come from one fertilized egg that split into two. Fraternal twins are two separate eggs fertilized by two separate sperm.Identical twins don't have to share a sac or placenta. It is possible for them to have their own if they split within the first three days of conception.
Fraternal twins tend to be caused by the mother's genetics, but can also be the result of fertility treatments or even a complete fluke. Identical twins are always a complete fluke.Twins "running" in the husband's family does not mean he and his wife are more likely to have twins. However, should such a couple have a daughter, she could be more likely to have twins.
It is possible to not know what type of twins one has. The only ways you can know for certain are to test their DNA (expensive!), the twins are a boy and a girl, or they shared a placenta and/or sac in utero.
I know I'm forgetting something, but it's late and I'm not thinking straight. If I remember more, I'll update this post. I realize that most of you already knew most or all of the above information. I also realize that most of you are probably not the type of people to ask silly genetics questions of complete strangers. But this is the only place I know where to start without having to make and print out pamphlets to hand out when someone asks me a question. So thanks for listening:)
Clarification: I don't mind being asked questions by complete strangers who are merely curious. I really don't have the time to stop and answer all of them, though. I'd much rather get my errands done and get home. Plus, if I start to answer questions they start to ask more and the questions get more and more personal. I'm not into letting a total stranger know the complete story of A and W or my medical history. We need our privacy just as much as the lady over there with three kids. I really don't mind being asked questions by family or friends; in fact, I welcome them. So I hope I didn't scare anybody off from asking me any questions related to twins or anything for that matter. If I know you, I'm more than happy to answer any questions. Bring 'em on.
Originally written: August 1, 2008