re: Well my step son decided to come out last night.

quote:

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I keep saying he must have got it from his daddy.

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FWIW, homosexuality in men is indeed genetic, but it is X-linked recessive (XLR), i.e. it is matrilineal in how it passes as it rides on the x chromosome. From an evolutionary standpoint, this makes sense, for homosexuality does not make a man more fit to pass on his genes.

With an XLR trait, however, a female needs two X chromosomes with the trait for it to show up, and as a result, a woman can be a carrier of homosexuality without manifesting any traits from it. This is what has prevented homosexuality from selecting itself out of the gene pool.

Conversely, a man only needs one tainted XLR chromosome, for the Y chromosome does not override the X. This is why it shows up in men.

TL;DR: Your stepson got it from his mom. Not his dad, as a matter of genetics.