A Lesson in Genetics

Posted by & filed under One Nice Thing About Today.

Lately, I have been hearing a lot of weird ideas about the genetics of having twins. I only took one biology class in college, but from my limited knowledge from that class I know people have been saying impossible things. The most common being “they say twins skip a generation” (There could be recessive traits that don’t show up as often as dominant traits, but they still wouldn’t skip generations each time.), and the most comical being “every eldest daughter on my husband’s side has twin boys” (too much wrong with that statement to even begin).

There are a few key points about twins genetics that help in understanding the situation:

  • Identical twins -where one egg splits into two babies- are NOT genetic. They’re just a fluke of nature.
  • Fraternal twins -where two eggs are released and become two babies- are only dependent on the woman’s genetics, because only her body decides when and if to release more that one egg.

So if a couple wants to know if they are likely to have twins, they should only look at the woman’s family genetic history.

But the father needn’t feel left out of all this twin-making business. He has an important job to do. It is his biology that determines the genders of the babies. Scott can fear all he wants that girls are going to be more complicated than boys, but it’s his fault we got two girls. Well, if they’re fraternal then I’ll have to remember it’s my fault there are two in the first place, when neither will sleep at 2am.

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