I guess penis size is certainly hereditary, but only in the sense we also inherit other body features from our parents, like body height, color of hair and of eyes, and so on. That penis size is inherited can be seen clearly in monozygotic twin brothers, whose genitals usually resemble very much.
The only problem with penis heritage is, that you will not see the results of the parents\' \"genes mixture\" immediately in every child, but only in boys. The genes to develop a penis are on chromosomes which are so-called autosomes, which means that they are not dependent on the sex of the person who carries them. They are equally present in men and women. So some inherited penis feature will remain \"hidden\" in a woman, and only when she gets pregnant with a son, the genes of her and her husbands grandparents (and not only their granddads!) come into effect.
But who knows the size of his granddads\' penises? And of the fathers of their grandmothers (who carried their parents\' penis genes hidden)?
What adds to complexity is that the developed size depends ONT ONLY on genes, but supposedly also on nutrition, severe diseases during childhood, hormonal status, hormon resistency and so on, which hinder the \"programmed size\" to fully develop.
I know my father\'s (
Flaccid) penis quite well (we were never shy in our family to show each other naked). It does not really resemble my penis, especially it is bigger in
Girth. His
Balls are also about twice the size of mine. The only thing we share is the prominent and thick glans. So I do not believe we can estimate the sizes of our sons\' dicks from our own, just with the argument of heredity.