The phrase "in blood" can refer to a familial relationship or a deep-seated connection. There are several synonyms that can be used to convey similar meanings. For example, the phrase "by birth" means the same thing as "in blood", or "by family ties". Other synonyms include "inherited", "inbred", and "lineal". Additionally, the phrase "in the genes" can be used to describe a trait or behavior that is passed down through generations, similar to the idea of "in blood". Overall, there are many ways to convey the concept of a strong, inherent connection or relationship, all of which can be used interchangeably with "in blood".