Original sentence: "  Rat fanciers have developed many exotic varieties.Besides ones with unusual colouring, there have been rats bred that have bigger Ears, no fur, no tails and oversized hind legs.Descendants of rats bred for research, these animals also are called "coloured rats" or "colour rats.Domesticated rat's tend to be both more docile than their wild ancestors and more disease prone, presumably due to inbreeding.In Western countries, many people keep domestic rats as pets.Like mice, rats (especially albino rattus norvegicus) are frequently subjects of medical, psychological and other biological experiments.Scientists have bred many strains or "lines" of rats specifically for experimentation.This is because they grow quickly to sexual maturity and because they are easy to keep and to breed in captivity
Edited sentence: Besides the fur colour, fanciers have bred rats with bigger Ears, without fur, tails and/or bigger back legs.Domesticated rat's are tamer than their wild ancestors and get cancer more quickly (as intended by lab researchers).If these attributes are positive for the animals remains doubtful.Like mice, rats (especially rattus norvegicus) are frequently the subjects of medical, psychological and other biological experiments.Many people keep descendandts of lab rats as pets; some fanciers have developed exotic varieties and colours of rat.Often enough there has been a strong incest breeding down the line, causing even more health problems.Scientists have bred many "lines" of rats specifically for experimentation.The domestic rat, in many ways, behaviour, fur color and health sensitivity, is also called Coloured Rat or Colour Rat.This is because they grow quickly to sexual maturity and they are easy to keep and to breed in captivity