A Pyr with single dew claws could carry a recessive gene for double dew claws. When mated with a female with double dew claws, the recessive gene could line up with a gene for double dew claws, so some of the puppies would have double dew claws. But, they would carry a recessive for single dew claws and could produce single dew claws on their offspring. Yes, it is very confusing. . .