A team of genetic scientists led by Dr Shu-Jin Luo from Peking University in Beijing, using whole-genome sequences of white and normally-colored Bengal tigers, has revealed that a mutation in a single pigment gene, called SLC45A2, is responsible for the unusual coloration of white tigers.

“The white tiger, an elusive Bengal tiger (Panthera tigris tigris) variant with white fur and dark stripes, has fascinated humans for centuries ever since its discovery in the jungles of India. Many white tigers in captivity are inbred in order to maintain this autosomal recessive trait and consequently suffer some health problems, leading to the controversial speculation that the white tiger mutation is perhaps a genetic defect,” the researchers explained in a paper published online in the journal Current Biology.

“However, the genetic basis of this phenotype remains unknown.”

In the new study, the scientists mapped the genomes of a family of 16 captive tigers, including both white and orange individuals. They then sequenced the whole genomes of each of the three parents in the family.

The genetic analysis led them to a pigment gene, called SLC45A2, which had already been associated with light coloration in some animals, including horses, chickens, and fish.

The gene variant found in the white tiger primarily inhibits the synthesis of red and yellow pigments but has little to no effect on black, which explains why white tigers still show characteristic dark stripes.

“The white tiger represents part of the natural genetic diversity of the tiger that is worth conserving, but is now seen only in captivity,” Dr Luo said.

The team advocates a proper captive management program to maintain a healthy Bengal tiger population including both white and orange tigers. “It might even be worth considering the reintroduction of white tigers into their wild habitat.”

Dr Luo said: “historical records of white tigers on the Indian subcontinent date back to the 1500s, but the last known free-ranging white tiger was shot in 1958. That many white tigers were hunted as mature adults suggests that they were fit to live in the wild. It’s worth considering that tigers’ chief prey species, such as deer, are likely colorblind.”

With the causal gene identified, the team hopes to explore the evolutionary forces that have maintained tigers in both orange and white varieties.

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Bibliographic information: Xiao Xu et al. The Genetic Basis of White Tigers. Current Biology, published online May 23, 2013; doi: 10.1016/j.cub.2013.04.054