Are White Tigers a Separate Species? The Genetics Explained

What makes a tiger white?

An orange tiger has two kinds of pigment in its fur. Pheomelanin produces the red, orange and yellow background, and eumelanin produces the black and dark brown stripes. A white tiger cannot make pheomelanin, so its background fur is white or cream, while the dark stripes remain.

In 2013 a team of researchers in China sequenced the genomes of a family of white and orange tigers and found the cause: a single change in a gene called SLC45A2, which codes for a protein that transports materials inside pigment cells. The mutation swaps one amino acid in the protein, apparently blocking it and preventing orange pigment from forming in the hair. Variants of the same gene cause light coat colors in horses and other animals and are linked to lighter skin in some human populations.

The same mutation also affects the eyes, which is why white tigers have blue eyes instead of the usual yellow-amber, and a pink nose.

How the white gene is inherited

The white trait is recessive. Every tiger carries two copies of the SLC45A2 gene, one from each parent:

• A tiger with two normal copies is orange.
• A tiger with one normal and one white copy is still orange but is a hidden carrier.
• A tiger with two white copies is white.

When two carriers breed, each cub has about a one-in-four chance of being white. When two white tigers breed, all the cubs are white. This explains why white tigers were always rare in the wild: the gene had to be passed down from both sides of a family.

Are white tigers albino?

No. True albinism, caused by a broken tyrosinase (TYR) gene, removes all melanin pigment. An albino animal is white all over, without dark markings, and usually has pink or very pale eyes. White tigers keep their dark stripes and have blue eyes, so they are better described as leucistic, a general term for reduced pigment. Only a very few true albino tigers have ever been reliably reported. The white lion’s pale coat, by contrast, does come from a milder mutation in the tyrosinase gene. A similar confusion surrounds other pale animals; see Are white peacocks albino?

The white tigers of Rewa

White tigers were reported from the wild in India for centuries, especially in the forests of the former princely state of Rewa, in what is now Madhya Pradesh. In 1951 the Maharaja of Rewa captured a young white male in the forests of Sidhi district and named him Mohan. Mohan was later bred with an orange daughter, and in 1958 they produced the first white cubs born in captivity.

Most white tigers in zoos today descend from Mohan. The last widely accepted wild white tiger was shot in 1958. Today a white tiger safari at Mukundpur, near Rewa, celebrates Mohan’s story, but it holds captive tigers rather than wild ones.

Inbreeding and health problems

Because the trait is recessive and white tigers were rare, breeders in India, the United States and Europe produced more of them by mating close relatives: fathers with daughters, brothers with sisters. Many American white tigers also have Amur tiger ancestry, mixed in from a part-Siberian male used in breeding.

Close inbreeding brings hidden harmful genes together. Captive white tigers and their orange siblings have suffered from cleft palates, spinal and kidney problems, poor immune function and high cub death rates. Many white tigers also have crossed eyes (strabismus); this is linked to the white gene itself, which changes how nerves from the eyes connect to the brain, much as in Siamese cats.

Snow-white tigers, with stripes so faint they are nearly invisible, arose in captivity through further inbreeding and combine the white gene with another color gene.

Why white tigers are not a conservation priority

Conservationists are clear that breeding white tigers does nothing to help wild tigers:

• White tigers are not a distinct population and do not represent any special part of tiger diversity.
• Most have unknown or mixed ancestry, so they cannot be used in breeding programs designed to keep wild bloodlines.
• Inbreeding to produce white cubs causes suffering and many unwanted orange cubs.
• A white coat stands out in the forest and would probably make hunting harder for a wild tiger.

For these reasons the Association of Zoos and Aquariums (AZA) in North America stopped its accredited zoos from intentionally breeding white tigers in 2011. Most white tigers today live in roadside zoos, private collections and entertainment venues.

Other tiger color variants

White is not the only unusual tiger color. Golden tigers have pale gold fur with reddish-brown stripes, caused by a different recessive gene. In Similipal Tiger Reserve in India, roughly a third of the tigers show pseudo-melanism, with stripes so broad they merge into dark patches. None of these forms is a separate species. To learn how the normal orange-and-black pattern works, see Why do tigers have stripes?