[RadioAstronomer]

If a particular attribute begins to develop such as feathers on early reptiles does the gene responsible for the previous skin mutate or is it replaced by the new gene

I have pinged a few folk who could better answer your question. I will still do a bit of research on the answer though. :-)

[Right Wing Professor]

If a particular attribute begins to develop such as feathers on early reptiles does the gene responsible for the previous skin mutate or is it replaced by the new gene

We can only make inferences about the genes of primitive birds. However, feather development in modern birds appears to be regulated by the same genes that control epidermal development (hairs, sweat glands, etc.) in mammals.

This is a comprehensive but very technical article. I'm not sure if it's freely available (I'm posting from work), but if it isn't, let me know and I'll brazenly violate copyright and post it.