in (one's) blood
Innate, as of a skill or quality. All of my relatives are doctors—medical prowess is just in our blood. She knows how to play. Music is in her blood.
in one's blood
Also, in the blood. Part of one's essential nature. For example, The whole family loves music; it's in their blood, or Sailing somehow gets in your blood. Also see run in the blood.
in (one's) blood
So characteristic as to seem inherited or passed down by family tradition.