X-Gene trick (read on - hard to explain in a sentence)
Okay, I discovered this at the first X-Gene I found, after meeting Toad. When I first found it, it was for Toad's poison aura. I quit before it saved and reloaded, continuing right before the X-Gene, and grabbed it again, but it was a Colossus gene this time. I did this again and it changed back to Toad, but a fourth time gave me a Psylocke defensive gene. A fifth time gave me a Pyro gene.
You can just keep doing this until you get the gene you want.