Plants can have the fast and slow metabolism genes at once

[Anticheese]

It seems like some genes should be mutually exclusive.

[I-Sett]

If the two cancel each other out (or even if not) this wouldn't seem to be unreasonable. Two different genes with the opposite effects can certainly be simultaneously promoted in the genome, such as an activator and an inhibitor of a particular pathway. And if they instead have a third effect, such as synthetic lethality, then damn, that's an awesome simulation of epistatic effects!
I say: Feature.

[UrsulaMejor]

this kind of stuff happens in real life and I think it's cool