White tiger: Encyclopedia II - White tiger - Inbreeding Depression

White tiger - Inbreeding Depression

Because the gene pool is so small, many white tigers suffer from health problems due to inbreeding. For this reason, responsible zoos refuse to breed two white tigers together. However, two white parents are the only way to ensure white cubs; if a white tiger mates with a partner that is heterozygous for the gene, only one in four of the offspring will be white. Thus, due to the high demand for white tigers, less scrupulous breeders still breed white tigers together. Some animal rights activists have called for a halt to the breeding of white tigers altogether.

Outside of India, highly inbred white tigers are prone to cross eyes (strabismus) due to incorrectly routed visual pathways in the brain), star-gazing and postural problems, a weakened immune system and poor tolerance of anaesthesia, possibly due to inability to synthesize the tyrosinase enzyme. Strabismus is associated with white tigers of Bengal/Amur ancestry. Only one pure Bengal white tiger was reported to be cross eyed, this being Mohini's daughter Rewati.

White tigers may also be prone to Chediak-Higashi Syndrome which causes bluish lightening of the fur colour and is associated with crossed eyes. Other genetic problems include shortened tendons of the forelegs, clubbed feet, central retinal degeneration, abnormal kidneys, arched or crooked backbone and twisted neck. Reduced fertility and miscarriages were noted by Sankhala and weere attributed to inbreeding depression. 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 have also been linked to poor diet.

White tigers tend to be larger than their orange (normal) relatives. This has led to suggestions that the gene promotes larger size and that the disadvantageous white colour in homozygoutes is a side effect. The Zoo Outreach Organization in Tamil Nadu, India maintains a white tiger studbook compiled by AK Roychoudhury of the Bose Institute in Calcutta.

Adapted from the Wikipedia article "Inbreeding Depression", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki