A big issue is turning on things that shouldn't be turned on. A good way to imagine the chromosomes is like they are independent scripts with blocks of code. Some of the code is functional, some of it is code rot that is best left commented out. When you get a mutation that breaks the processes keeping the integrity of this codebase together, you end up sometimes seeing chunks of code cut and pasted around where it shouldn't be. Chunks fused together or separated, inverted, duplicated, removed entirely. This might result in code that should normally be commented out becoming uncommented and causing a lot of harm to the host.