hereditary

“Hereditary” is the adjective for anything passed down through genes from parents to children. When people say a trait or condition “runs in the family” and is written into the DNA rather than merely shared by habit, they mean it is hereditary.

A hereditary characteristic is carried by genes present in the reproductive cells, so it can be transmitted to the next generation. This is the key distinction from an acquired characteristic, which an individual develops during life and which, because it is not written into the eggs or sperm, is not passed on genetically.

In medicine the word marks an important boundary. A hereditary disease arises from a gene variant inherited from one or both parents and may recur in relatives. A disease that is genetic but not hereditary can arise from a brand-new mutation in a single person, present in their own cells yet absent from their parents.

Calling something hereditary does not mean it is unavoidable or fixed. Many hereditary tendencies only raise the probability of an outcome, and their expression can depend heavily on environment, lifestyle, and other genes, so a hereditary risk is rarely a certain fate.