Wiktionary
genetic sexual attraction
n. a phenomenon of sexual attraction between relatives and family members who were not raised together
Wikipedia
Genetic sexual attraction
Genetic sexual attraction (GSA) is incest between close relatives, such as siblings or half-siblings, a parent and offspring, or first and second cousins, who first meet as adults.
The term was coined in the US in the late 1980s by Barbara Gonyo, the founder of Truth Seekers In Adoption, a Chicago-based support group for adoptees and their new-found relatives.