No need to start from scratch. Here, someone else already took a wolf and made you a perfectly serviceable sea-level dog. With some genetic tweaking, you can craft a powerful pet that isn't bothered by living on an oxygen-starved mountaintop. A few of the same tweaks to your DNA will even let you live there with it. This is no cockapoo or schnoodle. The Tibetan mastiff and the dog it was bred from, called the Chinese native dog, are ancient breeds, thousands of years old. Tibetan mastiffs live comfortably on the Tibetan Plateau, which with an average elevation of over 4,500 meters is nearly three times as high as Denver. Residents keep the bulky, athletic beasts as guard dogs. Chinese geneticist Ya-Ping Zhang, along with an international group of coauthors, wanted to know what mutations in canine DNA had created this altitude-loving breed. They gathered DNA from 32 Tibetan mastiffs, along with 20 Chinese native dogs and 14 wolves—the starting material. The scientists compared the three sets of genes by looking for one-letter changes called SNPs (short for single-nucleotide polymorphisms, but pronounced "snips," as if someone had spliced the genome together with scissors and tape). Among those variations, they looked for signs of selection: when a gene suddenly becomes advantageous (maybe because it makes you resistant to a new disease, or because humans decide they prefer pets with shorter ears), it spreads rapidly through the population, and often sweeps up surrounding DNA with it. This creates a signature chunkiness to the DNA that genetic analysis can spot. Zhang and his coauthors narrowed their focus onto a set of 33 variants that looked like they'd been strongly selected for between Chinese native dogs and Tibetan mastiffs. These mutations were in 11 genes, including 9 genes with clear relevance to living at the top of the world. Several of these genes have to do with energy metabolism. Turning the food we eat into energy requires oxygen, so in the thinner air of the mountains, it's a good idea to make that process more efficient. Another gene helps build hemoglobin, the molecule that chaperones oxygen through the bloodstream. One gene is involved in building new blood vessels, an important response to low oxygen. Another one of the mutated mastiff genes, for a molecule that builds up in oxygen-starved cells and helps coordinate their response, was familiar to the scientists because it's also turned up in studies of Tibetan people. In at least one case, dogs and humans seem to have adapted to low oxygen by altering the same gene. None of the other mutations the researchers identified were shared with humans or other animals. But there was plenty of overlap in the categories of genes. Changes in blood-vessel-building genes, for example, have been found in yaks, Tibetan antelopes, and Andean humans. Several genes related to hemoglobin have turned up in studies of Tibetans, as well as people who live in the highlands of Ethiopia. The details vary. But over and over again, evolution has solved the problem of living at high altitude in similar ways. This means humans were not only able to remake ourselves into mountain dwellers, but could bring our best friends with us—the yaks. No, just kidding; of course it's the dogs.
Image: by MrNiceGuy1113 (via Wikimedia Commons)
Li Y, Wu DD, Boyko AR, Wang GD, Wu SF, Irwin DM, & Zhang YP (2014). Population variation revealed high altitude adaptation of Tibetan Mastiffs. Molecular biology and evolution PMID: 24520091
