how do some chickens make a majority of “double yolk”?


I had a carton of eggs, so far 5/12 have contained a double yolk (there are 3 left) this seems well beyond the estimates for young/old chickens online and by their math, astronomically unlikely.

Are there reasons this may happen related to the chicken?

In: 7

Not really sure but when I was a kid, we always stopped at the egg store in town. They sold double yolk eggs by the dozen. I think they were from their own chickens. I just figured they had some of a special breed on site.

So, a quick google search has told me that in chickens, a double yolk is indicative of fraternal twins (whereas an identical twin would be two embryos developing in the same yolk if the egg was fertilized and went through gestation properly) – in humans we’ve found two genes that affect ovulation and in particular a variant that induces hyperovulation – this makes it more likely for a woman with that gene to produce fraternal twins.

This would suggest that a similar gene may be found in chickens, but I haven’t found anything that looks like research on the topic in the few minutes I’ve looked.

Older hens’s eggs are more likely to have double yolks. Some supermarkets select for those and sell them: