bred in the bone

[bred in the bone] {adj. phr.} Belonging to your nature or character, especially from early teaching or long habit; natural from belief or habit; believing deeply.

The Willett children's cleanness is bred in the bone.

Often used, with hyphens before the noun.

Joe is a bred-in-the-bone horseman; he has been riding since he was six.

Contrast: SKIN-DEEP.