Several mutants have a "no gene" attack. Why not a Neutral gene? Its corresponding attack will always do X damage, no bonus, no loss, against all genes. That would create the possibility of 24 new breedable mutants if there were a common and a rare with the Neutral gene as primary and secondary. No change to current weakness/strength chart needed.

Bingo could be expanded from just one normal card to bronze, silver and gold cards as well.

Instead of freezing excess mutants how about a dugout area where mutants could be standing by ready to be used in a fight? They wouldn't generate any credits. With the (assuming) continued increase in mutants there will come a day when we'll be forced to swap mutants in and out of the freezer depending on the enemy to be faced. Speaking for myself, that would be annoying.