Rare Brown Pandas Explained: Genetic Mutation Unveiled

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The giant panda, known for its iconic black-and-white pattern, is a symbol of wildlife conservation. But, a few unique pandas with brown-and-white fur have been spotted, living in a remote mountain range in China. Scientists have been digging into the genetic secrets behind their distinct appearance, and they might have just cracked the code.

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Recent studies involving genetic analysis of both wild and captive pandas suggest that the brown-and-white fur coloration is due to natural genetic variation, not inbreeding as previously thought in a shrinking panda population.

The very first brown panda known to us, a female named Dandan, was discovered by a local ranger in the Qinling Mountains of Shaanxi province back in March 1985. Dandan lived out her life in captivity, passing away in 2000.

Since the finding of Dandan, there’s been a total of 11 sightings of these brown pandas, as documented by news sources and personal accounts, according to new research published in the journal PNAS on March 4.

“The pattern of these brown pandas showing up time and again suggests this might be a heritable trait. But, the specific genetics at play were a mystery until now,” the authors stated.

The senior author of the study, Dr. Fuwen Wei, a professor at the Chinese Academy of Sciences’ Institute of Zoology, emphasizes that understanding this coloration is key to potentially breeding this variant in captivity. The conservation status for giant pandas is currently listed as vulnerable on the IUCN Red List.

The team focused on Qizai, the only brown panda known in captivity, who was rescued as a cub in 2009. Under the microscope, Qizai’s brown fur appeared to have fewer, smaller, and oddly shaped melanosomes compared to his black-and-white counterparts.

Genetic data from Qizai’s family, including scat from his wild mother and information from his son born in captivity, revealed that while none had brown fur, they all carried one copy of the recessive gene on Bace2, with Qizai inheriting two.

This gene plays a role similar to how recessive traits in humans, like blue eyes or red hair, can be passed down without always being expressed physically. Both parents need to carry and transmit the variant for it to show in offspring, as seen in Qizai’s case.

Dandan’s genome, preserved for over two decades, was also sequenced, showing the same recessive trait. An extensive analysis of 192 black-and-white pandas confirmed that the mutation responsible for brown fur was only found in pandas from the Qinling Mountains, not in those from Sichuan where most of China’s panda population lives.

Confirmation came when scientists edited the Bace2 gene in lab mice using CRISPR-Cas9. The edited mice exhibited lighter brown fur, pointing to the mutation’s impact on coloration.

Dr. Wei hypothesizes that the mutation is specific to the unique environment of the Qinling Mountains, which differs from the climate in Sichuan. It’s a natural variation, not a consequence of inbreeding, as the kinship analysis indicates no close relation between Qizai’s parents.

Associate professor Tiejun Wang from the University of Twente, who has also studied these unique pandas, views this discovery as a positive sign that the rare coloration is a natural occurrence, not a genetic bottleneck from inbreeding. Wang, who spent a decade working as a field ranger in the same mountains, commends the research team for their efforts to illuminate this intriguing scientific question.

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