in inbreeding thats one of the biggest things is deformities, and problems within. rats are born with no tails, no ears, no eyes, missing appendages, no reproductive organs, and lots of other weird things. its the same as in humans or any other animals inbreeding causes problems. im not saying that these will arise right away, i may take many generations but eventually it will happen and it will result from inbreeding. if you you must ask your vet and he will clarify and vouch for what im saying. believe me i watch alot of discovery channel and animal planet...lol