Free of most of the ethical concerns — and practical difficulties — associated with the practice of eugenics in humans, dog breeders are seizing on new genetic research to exert dominion over the canine gene pool. Companies with names like Vetgen and Healthgene have begun offering dozens of DNA tests to tailor the way dogs look, improve their health and, perhaps soon, enhance their athletic performance.

Some discoveries grow out of government-financed research aimed at improving human health. Others are paid for by breed clubs carrying out their mission to better their breeds. By screening their dogs’ DNA for desirable and undesirable traits that might appear in their offspring, breeders can make more informed decisions about which dogs to — or not to — mate.

But because genes are often tied to multiple traits, scientists warn, deliberate selection of certain ones can backfire. The gene responsible for those silver-coated Labradors, for example, is tied to skin problems.