Phrase(s): Blood will tell.
Prov. A person whose ancestors had certain characteristics, often bad ones, will eventually turn out to be similar. • Lisa’s father was a gambler, and now Lisa has started to gamble, too. Blood will tell. • William went to all the best schools, but he’s just as vulgar as the rest of his family. Blood will tell.
McGrawhill's American Idioms And Phrasal Verbs