 Some people do what's called line breeding
This is true with dogs, cats, birds, just about anything. For example, you could breed a female with her grandfather to try to bring out a particular outstanding characteristic they both possessed. I don't particularly like the idea. The more genetically similar animals (including humans) are, the more likely you are to bring out bad recessive genes. That doesn't necessarily mean an inviable puppy. It could be a seemingly normal puppy that's later found to have a genetic defect. Many of these are either expensive or impossible to correct.
(Just for a bit of trivia, this is the whole reason that it's now illegal in most, if not all, states to marry closer than a second or third cousin. I've met many people who think that's something the Christians forced on people because it's immoral. It has nothing to do with immorality. There was all kinds of incest in the Christian Bible. It evolved from the long-past French tradition of marrying only within the royal family. They finally figured out that's why so many of the male heirs were turning out to be hemophiliacs. Duh!) |