 Due to freedom in the way Castle was allowed to run the laboratory and his financial backing by the University they were able to create an extensive program in mammalian genetics.The mice turned out to be an almost perfect solution for test subjects for mammalian genetic research.The fact that they had been bred by ‘rat fanciers’ for hundreds of years allowed for diverse populations of an animal while the public held far less sentiment for these rodents than they did for dogs and cats.