The sad part is that you’re not too far off from many fields of research. For example, research in neurodegenerative diseases in humans tested on mouse models means acquiring mice with diseases that they can’t get. So, you instead use gene-edited or generically engineered mice that are designed to exhibit all of the symptoms of a human neurodegenerative disease, and then try changing those symptoms in the mice in hopes that you’ll learn something that can be translated to humans.