Washington: White tigers today are only seen in zoos, but they belong in nature, according to researchers who found new evidence about what makes them white.
Their spectacular white coats are produced by a single change in a known pigment gene, according to the study.
"The white tiger represents part of the natural genetic diversity of the tiger that is worth conserving, but is now seen only in captivity," Shu-Jin Luo of China`s Peking University said.
Luo, Xiao Xu, Ruiqiang Li, and their colleagues advocate a proper captive management program to maintain a healthy Bengal tiger population including both white and orange tigers.
They said that it might even be worth considering the reintroduction of white tigers into their wild habitat.
The researchers mapped the genomes of a family of 16 tigers living in Chimelong Safari Park, including both white and orange individuals.
They then sequenced the whole genomes of each of the three parents in the family.
Those genetic analyses led them to a pigment gene, called SLC45A2, which had already been associated with light coloration in modern Europeans and in other animals, including horses, chickens, and fish.
The 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.
Captive white tigers sometimes do show abnormalities, such as crossed eyes, but Luo says any frailties are likely the responsibility of humans, who have inbred the rare tigers in captivity.
With the causal gene identified, the researchers ultimately hope to explore the evolutionary forces that have maintained tigers in both orange and white varieties.
The study is published in the journal Current Biology, a Cell Press publication.