Q: –“If being gay is genetics, how is the gene passed down?”– AFAIK it’s the m

Q: –“If being gay is genetics, how is the gene passed down?”–
AFAIK it’s the mother’s in-utero reaction to the fetus. Whether this is due to hormonal or immune system reactions we don’t know but appears to be both. We do know that it does not provoke the miscarriage response.
AFAIK it has nothing to do with the fetus and everything to do with the mother. Which is why it runs in families.
Boys are more fragile in the first place because male brain is specialized by intentional developmental perturbation. Sexual differentiation in males acts as a controlled poisoning of the developmental process—sacrificing robustness to enable specialization.
This fragility is a cost of the evolutionary strategy of using male variability to test advantageous traits under evolutionary pressure.
Nature experiments with the male and saves successes via reproduction with females.