When people say “twins run in the family”, wouldn’t it have to run through the females of the family? If it does indeed run in families, what’s the SD on how this actually works?
Apparently a mother whose family has fraternal twins in it is more likely than most mothers to have fraternal twins. The father’s genetics is irrelevant. The chance for identical twins doesn’t increase if the mother’s family has identical twins in it:
That makes perfect sense for fraternal twins. For identical twins, I concluded this would be harder to reason out. So, I was on the right track. Thanks!
Family history matters only for fraternal twins, not for identical twins. That latter event comes from a single fertilized ovum splitting and then separating, an event that seems unrelated to genetics.
But fraternal twins are indeed a trait that can run in families. It need not be exclusively transmitted from mom to daughter, though. A dad with that family history can pass it on to his daughter, who may one day go on to have twins.
More details available here: Does genetics affect the chance of having twins?
I see Wendell Wagner beat me to the site, but let me re-iterate: Dad’s genetics do matter, if he passes the tendency to a daughter. Or to a son, who later passes it on to HIS daughter. Etc. It’s NOT an x-linked trait.
Or, as I often respond when somebody asks me if twins run in my family: “No, but they run in my IVF clinic.”
So… is it just a weird coincidence that my great-grandmother had twins and one of her sons did too? (one of her daughters did also, but that isn’t as coincidental). Neither of her children who had twins was themselves a twin, because unfortunately her twins didn’t survive a flu epidemic when they were two years old - all eight of their siblings lived though.
Coincidences happen. My Uncle D has two sons, both of whom were from twin pregnancies. The older son’s twin was present at the first ultrasound but stopped developing very early in the pregnancy, so the older son was a single birth. The younger son’s twin was lost at (iirc) 33 weeks due to pregnancy complications. Both twin pregnancies were the result of fertility treatments, which makes the older son going on to have (healthy, happy) twins naturally just pure coincidence.
I feel like 8 non-twin pregnancies suggests that she didn’t have a genetic proclivity toward twins.
I believe there’s also a slight increase in twin births as your approach menopause, separate from fertility treatments.
Just an added datum. Frequency of identical twins seems the same in all races, abpit 1in 300, IIRC. Frequency of fraternal twins varies from nearly 0 among East Asians to 1 in 75 among Europeans.