As Coop observes, one of the most surprising things is the very long tail of distributions for paternal grandparents. This is due to the lower recombination rates in males. Remember that recombination tends to reduce the variance in transmission from the grandparental generation, so reduced recombination increases the variance. Therefore, you see that 1 in 200 sperm are skewed such that 20% or less of genetic material in the sperm is from one grandparent. Because you have to divide this by half in the fertilized zygote, what this means that in 1 in 200 individuals you have a case where 10% or less of their genome is from one paternal grandparent, and 40% or more from the other! The histogram for females, as you can see, is much less dispersed, though the variation there is not trivial either. I suspect that the scientists at 23andMe almost certainly know the empirical distribution, as they likely have many pedigrees to compare. It would be nice if they shared that with us.