The closest thing to a gay gene
Not all physical conditions are expressed via genetics. We have things like epigenes, proteins and environmental factors and about a gazllion other things that change someone's "physical condition".
Without observing a person's behavior or asking them, how could you possibly determine sexual preference? It is not an objective condition
- What difference does it make if sexual orientation is objective or subjective, or both?
- How does the observableness of a thing affect it's subjectivity/objectivity?
- Who (other than self-righteous assholes) gives a flying fuck if being gay or straight is a choice?
- Has it ever occurred to you that the act of sex is a choice, but the preference for sexual partners isn't? I.e. someone is capable of choosing a sexual partner that isn't their preference?