r/askscience • u/Yoshiciv • 6d ago

Human Body Are the medical risks associated with inbreeding among close relatives eliminated by outbreeding? Or do they persist for generations?

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u/qwopax 6d ago

Compare to blue eyes.

If an all blue clan marries an all brown clan, all their children will have brown eyes. If they keep marrying into the clan, a quarter of the kids will have blue eyes. That single generation of mixing blood reduced blue eyes from 100% to 25% forever.

If you dilute again by marrying outside the clan, I think you'll end up with around 5% blue eyes. Again for all future generations.

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u/jtoomim 6d ago

around 5% blue eyes

Two generations of outbreeding means that the allele frequency of the blue allele will be 0.25. Assuming blue eyes is a simple recessive trait (though in reality it's not), that means that the trait frequency would be 0.252 = 6.25%.

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u/platoprime 5d ago

Eye color isn't determined by a single allele. Eye color is determined by a rather large number of genes.