A recent video from The Jolly Heretic suggested parents of mixed-race children are more closely related to a random stranger of their own ethnicity than their own children, according to PCA plots. However, parents always share 50% of their DNA with their children, mixed-race or not. How to reconcile this apparent contradiction, where your mixed-race children plot father away from you than a stranger of your own ethnicity, despite sharing less DNA with the latter?
You did your simulation wrong - it’s easy to see that under random mating that variance between midparents is half pop var & that within family variance provides the other half.
But if you rank order couples midparent variance is equal to population variance, assuming parent pedigrees are no similar & within family variance is unchanged, now a within family variance is now a third of population variance.
Basically you are doing your calculation relative to the wrong generation.
I'll probably follow up with a multigenerational simulation, but this one was explicitly to write sibling variance in terms of parent generation variance, and it's always 50% in this case. This is useful because if I know what a (genetic) SD of IQ means among my generation, and I make a bunch of kids, the genetic IQ SD of those kids will be 70% of the SD I observe among my generation. What you're referring to is that the new generation can have a higher total population variance, if assortment is high, making half of the parental generation variance < half of the new population variance.
I've gotten this question a number of times in fact.
A recent video from The Jolly Heretic suggested parents of mixed-race children are more closely related to a random stranger of their own ethnicity than their own children, according to PCA plots. However, parents always share 50% of their DNA with their children, mixed-race or not. How to reconcile this apparent contradiction, where your mixed-race children plot father away from you than a stranger of your own ethnicity, despite sharing less DNA with the latter?
You did your simulation wrong - it’s easy to see that under random mating that variance between midparents is half pop var & that within family variance provides the other half.
But if you rank order couples midparent variance is equal to population variance, assuming parent pedigrees are no similar & within family variance is unchanged, now a within family variance is now a third of population variance.
Basically you are doing your calculation relative to the wrong generation.
I'll probably follow up with a multigenerational simulation, but this one was explicitly to write sibling variance in terms of parent generation variance, and it's always 50% in this case. This is useful because if I know what a (genetic) SD of IQ means among my generation, and I make a bunch of kids, the genetic IQ SD of those kids will be 70% of the SD I observe among my generation. What you're referring to is that the new generation can have a higher total population variance, if assortment is high, making half of the parental generation variance < half of the new population variance.