And don't forget that genes are conditional. If the conditions aren't met then the gene will stay inactive, regardless of whether they are junk DNA or active DNA.
If a robot has a gene that becomes active when he has more than 15000 body (for example) and another gene that spends down body points if they exceed 10000 then the first gene will stay inactive.
It can still mutate though.
A relatively small change could make this gene active again in one sudden step.
Happens all the time in my sims.
:D PY :D