Blood Idioms (American idioms)

in his/her blood 

explanation : Refers to a trait or talent that someone seems to have naturally. It may be a talent that is present in the person's family (as in the expression, runs in the family). If a person has a grandfather and father in the army, we may say The army is in his blood.

e.g.  It's no wonder the Kenndeys always go into politics.
        It's in their blood!