Now that I think of it, it depends on exactly what it means for Omega to tell that you have a gene for two-boxing. If Omega has the equivalent of a textbook saying "gene AGTGCGTTACT leads to two-boxing" or if the gene produces a brain that is incapable of one-boxing at all in the same way that genes produce lungs that are incapable of breathing water, then what I said applies. If it's a gene for two-boxing because it causes the bearer to produce a specific chain of reasoning, and Omega knows it's a two-boxing gene because Omega has analyzed the chain and figured out that it leads to two-boxing, then there actually is no difference.

(This is complicated by the fact that the problem states that having the gene is statistically associated with two-boxing, which is neither of those. If the gene is only statistically associated with two-boxing, it might be that the gene makes the bearer likely to two-box in ways that are not implicated if the bearer reasons the problem out in full logical detail.)