The Panda's Genetic Puzzle
In 2009, an international team led by the Beijing Genomics Institute at Shenzhen (BGI-Shenzhen) published the first complete draft of the giant panda genome. The genetic material came from a three-year-old female panda named Jingjing, a resident of the Chengdu Research Base of Giant Panda Breeding and one of the mascots for the 2008 Beijing Olympics. The project sequenced all 2.4 billion DNA base pairs of her genome, which contains an estimated 21,000 protein-coding genes, a number similar to that of humans. This was the first time any bear species had its genome fully sequenced.
The central mystery the project sought to solve was why an animal belonging to the order Carnivora subsists almost entirely on bamboo. The answer was found not in what the panda genome has and in what it has lost. Researchers discovered that the gene Tas1r1, which codes for the umami (savory) taste receptor, is non-functional in pandas. Two mutations have turned it into a "pseudogene," meaning it is no longer expressed. This receptor is what allows carnivores and omnivores to perceive the savory flavor of amino acids in meat. Without it, pandas are essentially "taste-blind" to meat, which likely prompted their ancestors' shift to a vegetarian diet. Molecular dating estimates this genetic change occurred around 4.2 million years ago, a date that aligns with fossil evidence of the panda's dietary switch.