Now vs Million year back |white Tiger |#shorts #short #animals #discovery #youtubeshorts

The white tiger or bleached tiger is a leucistic pigmentation variant of the mainland Asian tiger. It is reported in the wild from time to time in the Indian states of Madhya Pradesh, Assam, West Bengal, Bihar, Odisha, in the Sunderbans region and especially in the former State of Rewa.[1] It has the typical black stripes of a tiger, but its coat is otherwise white or near-white.
The white Bengal tigers are distinctive due to the color of their fur. The white fur is caused by a lack of the pigment pheomelanin, which is found in Bengal tigers with orange color fur. When compared to Bengal tigers, the white Bengal tigers tend to grow faster and heavier than the orange Bengal tiger.[citation needed] They also tend to be somewhat bigger at birth, and as fully grown adults.[citation needed] White Bengal tigers are fully grown when they are 2–3 years of age. White male tigers reach weights of 200 to 230 kilograms (440 to 510 lb) and can grow up to 3 meters (9.8 ft) in length. As with all tigers, the white Bengal tiger's stripes are like fingerprints, with no two tigers having the same pattern. The stripes of the tiger are a pigmentation of the skin; if an individual were to be shaved, its distinctive coat pattern would still be visible.
For a white Bengal tiger to be born, both parents must carry the unusual gene for white colouring, which only happens naturally about once in 10,000 births.[2] Dark-striped white individuals are well-documented in the Bengal tiger subspecies (Panthera tigris) as well as having been reported historically in several other subspecies.[2] Currently, several hundred white tigers are in captivity worldwide, with about one hundred being found in India. Their unique white color fur has made them popular in entertainment showcasing exotic animals, and at zoos. Their rarity could be because the recessive allele is the result of a one-time mutation or because white tigers lack adequate camouflage, reducing their ability to stalk prey or avoid other predators.
A white tiger's pale coloration is due to the lack of the red and yellow pheomelanin pigments that normally produce the orange coloration.[3] This had long been attributed to a mutation in the gene for the tyrosinase (TYR) enzyme. A knockout mutation in this gene results in albinism, the ability to make neither pheomelanin (red and yellow pigments) nor eumelanin (black and brown pigments), while a less severe mutation in the same gene in other mammals results in selective loss of pheomelanin, the so-called Chinchilla trait. The white phenotype in tigers had been attributed to such a Chinchilla mutation in tyrosinase,[3][4][5] and in the past white tigers were sometimes referred to as 'partial albinos'.[4][6] While whole genome sequencing determined that such a TYR mutation is responsible for the white lion leucistic variant, a normal TYR gene was found in both white tigers and snow leopards.[7] Instead in white tigers a naturally-occurring point mutation in the SLC45A2 transport protein gene was found to underlie its pigmentation. The resultant single amino acid substitution introduces an alanine residue that protrudes into the transport protein's central passageway, apparently blocking it, and by a mechanism yet to be determined this prevents pheomelanin expression in the fur.[3] Mutations in the same gene are known to result in 'cream' coloration in horses,[3] and play a role in the paler skin of humans of European descent.[8] This is a recessive trait, meaning that it is only seen in individuals that are homozygous for this mutation,[3] and that while the progeny of white tigers will all be white, white tigers can be also bred from colored Bengal tiger pairs in which each possesses a single copy of the unique mutation.[9][7] Inbreeding promotes recessive traits and has been used as a strategy to produce white tigers in captivity, but this has also resulted in a range of other genetic defects.

The stripe color varies due to the influence and interaction of other genes. 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, 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.[10] Kailash Sankhala observed that white tigers were always whiter in Rewa State, even when they were born in New Delhi and returned there. "In spite of living in a dusty courtyard, they were always snow white."[11] A weakened immune system is directly linked to reduced pigmentation in white tigers.