blood relationship; blood ties
Refers to a relationship by blood, as opposed to marriage or adoption. Often used in contexts emphasizing family lineage or genetic connection.
I'm not related to him by blood, but I feel like he's my real brother.
Blood ties are not the only bonds of family.
Standard spelling using kana for つながり; the most common written form.
Kanji spelling for つながり; less common but still encountered.
Compound of 血 (ち, 'blood') + の (possessive particle) + つながり (connection, relationship). The reading つながり is the nominalized form of the verb つながる (to be connected).