expression, noun-modifying (irregular)
related by blood; blood-related
Used as a prenominal modifier to describe family members connected by blood, not by marriage or adoption.
彼は血の繋がった兄弟のように思っている。
He thinks of him as a blood-related brother.
血の繋がった親子でも、考え方は違う。
Even blood-related parents and children have different ways of thinking.
血縁 is a formal noun meaning 'blood relation' or 'consanguinity', while 血の繋がった is a more colloquial, descriptive phrase used attributively.
A phrase composed of 血 (blood), の (possessive particle), and 繋がった (past form of 繋がる, 'to be connected'). Literally 'connected by blood'.