Tuesday, April 20, 2010

White Tigers

THE WHITE TIGERS





                                                                     


A white tiger is a tiger with a recessive gene that creates the pale coloration. 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.

Compared to orange tigers without the white gene, white tigers tend to be larger both at birth and at full adult size.This may have given them an advantage in the wild despite their unusual coloration. Heterozygous orange tigers also tend to be larger than other orange tigers. Kailash Sankhala, the director of the New Delhi Zoo in the 1960s, said "One of the functions of the white gene may have been to keep a size gene in the population, in case it's ever needed."
Compared to orange tigers without the white gene, white tigers tend to be larger both at birth and at full adult size.This may have given them an advantage in the wild despite their unusual coloration. Heterozygous orange tigers also tend to be larger than other orange tigers. Kailash Sankhala, the director of the New Delhi Zoo in the 1960s, said "One of the functions of the white gene may have been to keep a size gene in the population, in case it's ever needed."




 

Dark-striped white individuals are well-documented in the Bengal Tiger subspecies, also known as the Royal Bengal or Indian tiger, (Panthera tigris tigris or P. t. bengalensis), may also have occurred in captive Siberian Tigers (Panthera tigris altaica), and may have been reported historically in several other subspecies. White pelage is most closely associated with the Bengal, or Indian subspecies. Currently, several hundred white tigers are in captivity worldwide with about 100 of them in India, and their numbers are on the increase. The modern population includes both pure Bengals and hybrid Bengal–Siberians, but it is unclear whether the recessive gene for white came only from Bengals, or from any of the Siberian ancestors as well.

The unusual coloration of white tigers has made them popular in zoos and entertainment that showcases exotic animals. The magicians Siegfried & Roy are famous for having bred and trained two white tigers for their performances, referring to them as "royal white tigers" perhaps from the white tiger's association with the Maharaja of Rewa. The exotic-tiger performance trio of Ron Holiday, Joy Holiday and Chuck Lizza—subjects of the HBO documentary film Cat Dancers—worked with a white tiger which ended up killing two of them.

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