Is it true that if a dog has puppies and then you keep one if you mate the puppy with the father does this make the blood line thick meaning does it make a better breed or does this cause problems as it does in humans

Interbreeding like that concentrates the genes. It increases the chances of the offspring inheriting the same 2 recessive genes. This can be good or bad. At least with dogs, bad results can be discarded. Good ones can be bred further. Perhaps all yellow Labs trace back to one male in England. To produce more yellow Labs he was bred to his daughters.

I hope this is just a question out of curiosity. A general Q&A site such as AMHD is totally inadequate when it comes educating yourself in order to do quality breeding. http://www.woodhavenlabs.com/images/breeding-off.jpg is a step forward, but you really need to read some books starting with say Successful Dog Breeding, by Chris Walkowicz, DMV You should also read some books devoted to the breed you are interested in. Many others here and I, actually anybody that knows and loves dogs, hate the results from those that don't know or care enough to do it right. It is tough for us to be nice to people abusing dogs through poor breeding practices.