To avoid inbreeding among the world’s 333 captive pandas — more than 90 percent of which live in China — Ballou rates each one on a “mean kinship value” scale, which ranks how saturated the pool is with a particular panda’s genes. A low value means its genes are underrepresented, so it would be a good match, genetically speaking. A high value signifies overrepresentation, meaning he or she has made quite enough matches already.

Pan Pan, who lives in the Ya’an Breeding Center in China, has sired at least 32 cubs since his capture in the mid-
1980s and is the greatest example of overrepresentation. Tian Tian is one of his cubs.

Reproductive years generally fall between age 6 and 20. The life span of wild pandas is unknown, but captive animals have reportedly lived to age 35.

Pandas that are unhealthy and/or too old to breed — age 20 for females; older for some males — are excluded as potential matches. The National Zoo has a loan agreement with the State Forestry Administration, which owns pandas at the Ya’an Breeding Center and other locations in China. Ballou narrows
the field of eligible pandas down
to those living in the Ya’an facility.

Ballou uses the mean kinship values to come up with a “mate suitability index” specific to Mei Xiang and Tian Tian, based on how each pairing would affect the overall gene pool. A ranking of 1 is best; 6 is worst. Ballou says China would then choose potential mates based on this ranking plus age, location and temperament. Here are a few possible panda pairings provided
by Ballou.

Mei Xiang’s viability for pregnancy is statistically low because she has been involved in several unsuccessful attempts.

Thanks to his dad, Tian Tian’s genes are already abundant in the panda pool, so the MSI rank of potential matches will be higher.

SOURCE: Jonathan D. Ballou, Population Manager for the Smithsonian Conservation Biology Institute; Xie Zhong of the Chinese Association of Zoological Gardens. Photos by The Washington Post.