Genetic Relation Between Random Whites and a Mixed Couple With a Mixed Child

Topic Suggestion/Request:
(should match post title)

Genetic Relation Between Random Whites and a Mixed Couple With a Mixed Child.

Reasoning:
(why should this be covered)

Could you explain how a White father with a child born from a marriage to a black woman is more genetically related to any random White man than his own child? Yes, the child is 50% his, but what else is creating this distance between him and his child?