A white tiger's pale coloration is caused by the presence of a recessive gene. Another genetic characteristic makes the stripes of the tiger very pale; white tigers of this type are called snow-white or "pure white". White tigers are not albinos and do not constitute a separate subspecies of their own and can breed with orange ones, although (approx.) half of the resulting offspring will be heterozygous for the recessive white gene, and their fur will be orange. The only exception would be if the orange parent was itself already a heterozygous tiger, which would give each cub a 50% chance of being either double-recessive white or heterozygous orange. If two heterozygous tigers, or heterozygotes, breed on average 25% of their offspring will be white, 50% will be heterozygous orange (white gene carriers) and 25% will be homozygous orange, with no white genes. In the 1970s a pair of heterozygous orange tigers named Sashi and Ravi produced 13 cubs in Alipore Zoo, of which 3 were white. If two white tigers breed, 100% of their cubs will be homozygous white tigers. A tiger which is homozygous for the white gene may also be heterozygous or homozygous for many different genes. The question of whether a tiger is heterozygous (a heterozygote) or homozygous (a homozygote) depends on the context of which gene is being discussed. Inbreeding promotes homozygosity and has been used as a strategy to produce white tigers.
Contrary to popular belief, white tigers are not albinos; true albino tigers would have no stripes. Even the "stripeless" white tigers known today actually have very pale stripes.
Part of the confusion is due to the misidentification of the so-called chinchilla gene (for white) as an allele of the albino series (publications prior to the 1980s refer to it as an albino gene). The mutation is recessive to normal color, which means that two orange tigers carrying the mutant gene may produce white offspring, and white tigers bred together will produce only white cubs. The stripe color varies due to the influence and interaction of other genes.
While the inhibitor ("chinchilla") gene affects the color of the hair shaft, there is a separate "wide-band" gene affecting the distance between the dark bands of color on agouti hairs. An orange tiger who inherits two copies of this wide-band gene becomes a golden tabby; a white who inherits two copies becomes almost or completely stripeless. Inbreeding allows the effect of recessive genes to show up, hence the ground and stripe color variations among white tigers.
As early as 1907, naturalist Richard Lydeker doubted the existence of albino tigers. However, we do have a report of true albinism: in 1922, two pink-eyed albino cubs were shot along with their mother at Mica Camp, Tisri, in the Cooch Behar district, according to Victor N. Narayan in a "Miscellaneous Note" in the Journal of the Bombay Natural History Society. The albinos were described as sickly-looking sub-adults, with extended necks and pink eyes.
White tigers, Siamese cats, and Himalayan rabbits have enzymes in their fur which react to temperature, causing them to grow darker in the cold. A white tiger named Mohini was whiter than her relatives in the Bristol Zoo, who showed more cream tones. This may have been because she spent less time outdoors in the winter. White tigers produce a mutated form of tyrosinase, an enzyme used in the production of melanin, which only functions at certain temperatures (below 98° Fahrenheit). This is why Siamese cats and Himalayan rabbits are darker on their faces, ears, legs, and tails (the color points), where the cold penetrates more easily. This is called acromelanism, and other cats breeds derived from the Siamese, such as the Himalayan and the snowshoe cat, also exhibit the condition. K.S. Sankhala, who was director of the New Delhi Zoo in the 1960s, observed that white tigers were always whiter in Rewa, even when they were born in New Delhi and returned there. "In spite of living in a dusty courtyard, they were always snow white." A weakened immune system is directly linked to reduced pigmentation in white tigers.
Outside of India, white tigers have been prone to crossed eyes, a condition known as strabismus, an example of which is "Clarence the cross-eyed lion", due to incorrectly routed visual pathways in the brains of white tigers. When stressed or confused, all white tigers cross their eyes, according to tiger trainer Andy Goldfarb. Strabismus is associated with white tigers of mixed Bengal/Siberian ancestry. The only pure-Bengal white tiger reported to be cross-eyed was Mohini's daughter Rewati. Strabismus is directly linked to the white gene and is not a separate consequence of inbreeding. The orange littermates of white tigers are not prone to strabismus. Siamese cats and albinos of every species which have been studied all exhibits the same visual pathway abnormality found in white tigers. Siamese cats are also sometimes cross-eyed, as are some albino ferrets. The visual pathway abnormality was first documented in white tigers in the brain of a white tiger called Moni after he died, although his eyes were of normal alignment. The abnormality is that there is a disruption in the optic chiasm. The examination of Moni's brain suggested the disruption is less severe in white tigers than it is in Siamese cats. Because of the visual pathway abnormality, by which some of the optic nerves are routed to the wrong side of the brain, white tigers have a problem with spatial orientation, and bump into things until they learn to compensate. Some tigers compensate by crossing their eyes. When the neurons pass from the retina to the brain and reach the optic chiasma, some cross and some do not, so that visual images are projected to the wrong hemisphere of the brain. White tigers cannot see as well as normal tigers and suffer from photophobia, like albinos.
There is a 450 lbs. male cross-eyed white tiger, named Namaste, at the Pana'ewa Rainforest Zoo in Hawaii, which was donated to the zoo by Las Vegas magician Dirk Arthur. There is a picture of a white tiger which appears to be cross-eyed on just one side in Siegfried & Roy's book Mastering The Impossible. A white tiger, named Scarlett O'Hara, who was Tony's sister, was cross-eyed only on the right side. Scarlett was the only one of three white tigers born at Kingdoms 3, the Henry County, and Georgia Animal Park in June 1977 to survive. Scarlett was to have undergone an operation to tighten and loosen two muscles to turn the eye straight, which is a fairly routine operation in humans. She was sent to the Grady Memorial Hospital's animal research clinic in Atlanta. Her owner, Baron Julius Von Uhl, was the lion tamer at the park, and his ophthalmologist was to perform the surgery. Scarlett had an adverse reaction to the anaesthesia and died. The Atlanta Zoo veterinarian Morton Silberman said "There is always a chance of there being other genetic defects" and some of these could have affected her ability to withstand anaesthesia. Tiger trainer Alan Gold said that attempts to correct crossed eyes in white tigers through surgery have been unsuccessful because the problem is not in their eyes, it's in their brain. White tigers with crossed eyes are not always born that way; they may develop the condition later in life. Ika, one of the male white tigers from Kesari's 1976 litter, was not cross-eyed as a cub. He developed strabismus later on. Rewati was also not cross-eyed as a cub. Cincinnati Zoo director Ed Maruska commented on white tigers having crossed eyes: "In 52 white tiger births, there were four cases of strabismus, all from the four white offspring of Kesari and Tony. Bhim and Sumita (siblings) were retained and all of their offspring had normal set eyes except one male from their first litter. Because strabismus is of rare occurrence and probably linked to the white coat gene, it is probable that it might be further reduced or even eliminated by selective breeding." A male white tiger named Cheytan, a son of Bhim and Sumita born at the Cincinnati Zoo, died at the San Antonio Zoo in 1992 from anaesthesia complications during a root canal. It appears that white tigers also react strangely to anaesthesia. The best drug for immobilizing a tiger is CI 744, but a few tigers, white ones in particular, undergo a re-sedation effect 24–36 hours later. This is due to their inability to produce normal tyrosinase, a trait they share with albinos, according to zoo veterinarian David Taylor. He treated a pair of white tigers from the Cincinnati Zoo at Fritz Wurm's safari park in Stukenbrock, Germany, for salmonella poisoning, which reacted strangely to the anaesthesia.
Mohini was checked for Chédiak-Higashi syndrome in 1960, but the results were inconclusive. This condition is similar to albino mutations and causes bluish lightening of the fur colour, crossed eyes, and prolonged bleeding after surgery. Also, in the event of an injury, the blood is slow to coagulate. This condition has been observed in domestic cats, but there has never been a case of a white tiger having Chédiak-Higashi syndrome. There has been a single case of a white tiger having central retinal degeneration, reported from the Milwaukee County Zoo, which could be related to reduce pigmentation in the eye. The white tiger in question was a male named Mota on loan from the Cincinnati Zoo.
There is a myth, that white tigers have an 80% infant mortality rate. However, the infant mortality rate for white tigers is no higher than it is for normal orange tigers bred in captivity. Cincinnati Zoo director Ed Maruska said: "We have not experienced premature death among our white tigers. Forty-two animals born in our collection are still alive. Mohan, a large white tiger, died just short of his 20th birthday, an enviable age for a male of any subspecies, since most males live shorter captive lives. Premature deaths in other collections may be artifacts of captive environmental conditions... In 52 births we had four stillbirths, one of which was an unexplained loss. We lost two additional cubs from viral pneumonia, which is not excessive. Without data from non-inbred tiger lines, it is difficult to determine whether this number is high or low with any degree of accuracy. " Ed Maruska also addressed the issue of deformities: "Other than a case of hip dysplasia that occurred in a male white tiger, we have not encountered any other body deformities or any physiological or neurological disorders. Some of these reported maladies in mutant tigers in other collections may be a direct result of inbreeding or improper rearing management of tigers generally."
Other genetic problems include shortened tendons of the forelegs, club foot , kidney problems, arched or crooked backbone and twisted neck. Reduced fertility and miscarriages, noted by”tiger man” Kailash Sankhala in pure-Bengal white tigers were attributed to inbreeding depression. A condition known as "star-gazing", which is associated with inbreeding in big cats, has also been reported in white tigers. Some of the white tigers born to North American lines have bulldog faces with a snub nose, jutting jaw, domed head and wide-set eyes with an indentation between the eyes. However, some of these traits may be linked to poor diet rather than inbreeding.
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