You may not think very much about yaks, but Tibetans do.
The domestic yak is crucial for their survival on the harsh Qinghai-Tibetan Plateau. The yak provides meat, milk and, to the distate of many Western travelers, salty yak-butter tea. Like the people who domesticated it, the yak is tough, thriving at altitudes and with nutritional restrictions which can kill the common cow.
A recent study of the yak genome sheds light on what makes these beasts so well-suited for their hard lives on the high plateaus. The work, published in a recent issue of Nature Genetics, may also help shed light on how humans adjust to high altitude.
The newly published yak genome is the work of an international team of researchers headed Qiang Qiu and Jianquan Liu at the Lanzhou University in China. This first draft of the yak genome proved, unsurprisingly, similar to the already-known cattle genome. Indeed, the average protein similarity between yak and cattle is 99.5%. Genetic analysis of these two genomes suggest that yaks and cattle diverged approximately 4.9 million years ago, which is comparable to the time at which humans and chimps diverged.
It is, however, the differences rather than the similarities between yaks and cattle which are most illuminating. The researchers found that three genes related to hypoxia response were selected for in yaks but not in cattle. Hypoxia is a condition triggered by low oxygen and is a serious concern for cattle living in high-altitude, low-oxygen environments. One of the yak hypoxia genes (ADAM17) is particularly interesting because certain mutations in the human version of this gene are more common in high-elevation Tibetans than those living at lower elevations.
In addition to genes involved in hypoxia response, yaks seem especially evolved to deal with nutritional hardships. The researchers found five genes selected for in yaks that help them deal with limited food resources. These genes help yaks metabolize sugars, fats and proteins as well as regulate the amount of stomach acid produced and perhaps help the yak utilize nitrogen better.
The yak is an adaptive creature, and its genetic differences from cattle help clarify how they manage to live on the harsh, high plateaus. Although more research is needed, the yak and his DNA may eventually provide a window into better understanding high altitude sickness in humans. Now, I’d drink some [yak-butter tea] to that!