Giant panda genome unveiled

DNA clues suggest little inbreeding, surprise on the bamboo diet

What’s black and white and read all over? The giant panda genome. All 2.4 billion DNA base pairs of a 3-year-old female panda named Jingjing have been cataloged, researchers report online December 13 in Nature. The information will help researchers understand panda traits such as finicky diets. A thorough understanding of panda genetics may aid conservation efforts for the endangered bear.

GENE FOR CUTENESS? Decoding of the panda genome is based on DNA from the panda Jingjing. Photo: Zhihe Zhang

“I was really thrilled to read this,” says conservation scientist Donald Lindburg, former head of the Office of Giant Panda Conservation at the Zoological Society of San Diego.

An international consortium led by scientists in China found that the panda genome is smaller than the human genome, which comprises about 3 billion base pairs. Despite the difference in total size, the panda genome contains an estimated 21,000 genes that encode proteins, a number similar to that of humans.

Surprisingly, the panda genome turned up no signs of inbreeding. Jingjing’s two copies of DNA in each of her cells differed in many places, demonstrating a surprisingly high rate of heterozygosity. That finding suggests that the decline of the panda population has not been caused by inbreeding, says study coauthor Jun Wang of BGI-Shenzhen in China and the University of Copenhagen. Jingjing, named for the 2008 Beijing Olympic Games mascot, has a mixed genetic heritage from two regions of wild giant pandas in China, so her genome may be more diverse than that of other pandas, Wang notes.

Although the team found high diversity between the two copies of Jingjing’s DNA, other genetic studies indicate that pandas’ genetic makeup changes less from generation to generation than that of humans and other mammals, rendering the rate of evolution slower. This slow rate of evolution is consistent with the notion that the panda is a “living fossil,” says Wang.

The panda genome gives clues to understanding the panda’s strict bamboo diet. It turns out that pandas have mutations in two copies of a taste gene called T1R1, which encodes a protein that senses the savory taste of meats, cheeses, broths and other high-protein foods. These mutations may have robbed pandas of the ability to taste meat, pushing them toward their bamboo diet, the researchers suggest.

Pandas possess all the requisite genes for digesting meat, but none of the genes required for digesting bamboo, Wang and colleagues found. The researchers guess that pandas rely entirely on communities of gut microbes for extracting nutrients from bamboo.

Microbiome expert Julie Segre of the National Human Genome Research Institute in Bethesda, Md., calls the result fascinating and says that it “underscores the concept that the panda — and similarly the human — genetic landscape is truly made up of their own organismal and microbial genomes.”

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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