can you breed two dogs with the same father, but not the same mother?

That's still line breeding. Half the genes come from either parent.

i breed german shepherds. so yes you can breed them.

It's possible to breed half-litter mates....it's called line breeding which many breeders do in order to "set type" ...but..only after a long & careful study of each dog's bloodlines, pedigreed ancestors, phenotype (the dog you actually see) and genotype ( what you don't see that's lurking in the dog's genetic makeup of his ancestors) Actually, all "line breeding" is a form of "in-breeding' ..it's just the intensity that differs...full brother & sister being the most intense form of inbreeding..& totally unrelated dogs ( with no common ancestors in the last 3 generations) being an "out cross" which can, in many cases, be just as unpredictable in the outcome of the offspring, in the game of genetic roulette!

I would have to agree with the Golden Breeder on this,but to add that "mental retardation"might be something to think about seriosly.Although the dog may look and act fine,do you really Know for sure that one day something might happen quite unexpectedly trigger an unwanted reaction from this dog,2yrs and 150lbs later?or even a friends tiny dog might tear off a bottom lip when cuddled by an admiring person.Ive seen both.Sign me,dog behaviorist/trainer/breeder since 86.

Well it's good for reproduction but at the same time...it's BAD because there's interbreeding and it's not good. If you use the same father, there's a chance of mental retardation and also there will be an DNA deficiency since the dog and the father share the same DNA. It will give the puppies alot of health problems....