Though it is not practical to eliminate all deleterious mutation, the incidence of affected individuals may be significantly reduced through a combination of intelligent breeding practice and the development of DNA tests. Mutations are changes in an organism's DNA that potentially affect the correct functioning of genes.
Mutations can occur anywhere in the DNA and in any cell.
Even though the DNA replication enzymes are very accurate, and there are also supplementary systems for detecting and correcting damage, no system is perfect. We should, therefore, recognize that some level of mutation is inevitable. However, the mutation rate is increased by radiation, including ultraviolet light, and exposure to certain toxic chemicals. The mutation rate for dogs cannot be determined readily, but from indirect evidence and extrapolation from other species, geneticists believe that mutation rates are normally on the order of 1 in 100,000 or less. For a sexually reproducing mammal, that would mean a new mutation in a particular gene would likely not occur more often than once in every 100,000 gametes.