Coding Difficulty: I'd say medium?
Have people enter shifts with their randomly generated "base genes" (as it is now), but make it so you have like, a 20% chance to spawn with a disability. If you fall within that 20%, then roll another check for how many disabilities you should get - 80% for 1 disability, 15% for 2 disabilities - 5% for 3 disabilities.
No EXTREME disabilities should be able to be randomly assigned on shift start to avoid people being mutes/have non-working legs/being radioactive at round start. They should be mild, but not major, annoyances - Like chronic cough, being Swedish, having a constant twitch.
This would make it so genetics have a little more to do than experimenting with monkeys - People would turn up at their doorstep wanting to be fixed. Additionally, it'd help genetics identify which blocks are disabilities, which would introduce another gene-meta other than the unstable mutagen one.
Also, to avoid cheesing of this mechanic - Mutadone should not be able to flush all of your genes to get rid of all of your disabilities. It'd instead revert your genes to the state of which you got at the round start - So if you have chronic cough at round start randomly generated, popping mutadone would reset everything else but that chronic cough, so only way to get it removed is by going to genetics.
Justification: A bit more to do for genetics, and nobody is created perfect, every human is more or less imperfect in their own way and everybody got a "quirk" to their character. Sure it is annoying a bit, but we don't get to chooses how they turn out when they're born - Right now disabilities are defects of rads causing mutation, nobody willingly will choose to be color-blind - Now imagine an engineer spawning with the color-blindness trait and him having to rush to genetics, would make a fun (for genetics) and emergent gameplay moment