But for certain, God didn't make thorns and thistles as part of the creation either, but they showed up later for the reason mentioned... We did that.
I'm glad to know I had a part in the creation of thorns and thistles.
So, everything bad in the world is Man's fault. Or more specifically, "first man's" fault. (Again seems like a God punishing an entire planet for one man's mistake is not such a nice God.)
But to go back to the GLO gene - by your account Adam's best bud Skippy the Chimp was sitting next to him at lunch when Adam got zapped by the God's anti-GLO ray. Skippy's mutation was just collateral damage (shouldn't God have better aim?).
Then what about guinea pigs and fruit bats? They both have non-functional GLO genes, but with different mutations than humans and chimps. How does God making guinea pigs and fruit bats scurvy-prone fit into your story?