I think it's incorrect to say they "revert to their wild genes". It's more a change in their outer appearance and traits while their genetics remains largely un

I think it's incorrect to say they "revert to their wild genes". It's more a change in their outer appearance and traits while their genetics remains largely untouched (at least over only a few generations). Revert also implies the scaling back of features, but evolution is blind and there is no such thing as "better", merely things that do better in the environment as it is right now. The glowing gene will be GFP which is a gene from jellyfish which has been introduced into these fish. So if any mutation suppresses or "turns off" the GFP gene, and GFP is maladative, then those fish will quickly outbreed their glowing siblings. The weird thing here, is the GFP gene will probably still be in their genome, it will just have a couple of errors that completely break it. I haven't heard of the goldfish example so I can't comment much on that. Except to say that I wonder if the "reversion" is because goldfish are inter-breeding with wild carp? Maybe not, and it is a mix of strong selection pressure and epigenetics causing the phenotypic change.