If your bitch gets pregnant by her son from a previous litter ,then this is an incestuous close, first degree mating. All pedigree dog breeds in fact come from an ancestry of close incestuous 1st degree matings, sibling matings, parent and child and the 2nd degree mating of grandparent to grandchild. This and other selective procedures are what establishes any given breed as a breed is genetically modified but through artificial selection processes and is therefore manmade .
Most breeds have their own specific serious diseases through the incestuous matings used and it is now a hugh dilemma as breeds are in fact "A parade of mutants" as some vets. Have described them.
You ask what happens, well normal pups can be born BUT incest brings together two copies of the mutated recessive allele that the shared ancestor of the incestuous mating parents has passed onto both the dam and the sire ( in your case the mum and her son ) The pup or pups that inherit a double mutated copy ,one from each parent, then inherits the mutation. This is why offspring of related parents can suffer genetic diseases.
Most breeds have their own specific serious diseases through the incestuous matings used and it is now a hugh dilemma as breeds are in fact "A parade of mutants" as some vets. Have described them.
You ask what happens, well normal pups can be born BUT incest brings together two copies of the mutated recessive allele that the shared ancestor of the incestuous mating parents has passed onto both the dam and the sire ( in your case the mum and her son ) The pup or pups that inherit a double mutated copy ,one from each parent, then inherits the mutation. This is why offspring of related parents can suffer genetic diseases.