LOL I think the mangaka made it a joke?
But I learned in my psychology uni lecture that it's considered a possible theory. They found some evidence on it though but not totally proven that being gay is hereditary.
Some scientists also think that some males can end up gay when they are in their mothers stomach. They think that the female hormones can make them more female and like boys not females.
Ummm, only the baka ones. If hormone levels affected a fetus, no males would be born straight. Sexuality can be affected genetically - in DNA - but hormones are transient and fluctuate to frequently to be a basis for sexuality. IOW They are a symptom of one's sexuality not the cause.
There is anecdotal evidence that homosexuality is hereditary, leading to greater research into the subject among geneticists.
"You know that gay is hereditary, right" ?
... Is it some kind of joke ?