London, July 20 : They say white horses are a mythical image of purity and sanctity. Now, a group of scientists have come up with a scientific answer for the white colour mystery.
Researchers at Uppsala University in Sweden say that the white colour of these horses is a result of a defective gene called "greying with age" gene.
In their study, the scientists have claimed that white horses are in reality mutants whose defective DNA carries a gene that speeds up ageing and rapidly turns their coats grey.
The study's key finding is that almost all white horses apparently carry an identical gene, which indicates that they all belonged to a single common ancestor.
It's not easy for white horses to survive in the wild as the white colouring makes them easy prey for predators, while the gene sharply raises the risk of such horses getting skin cancer.
This led the researchers to conclude that humans probably intervened to make sure they flourished.
"It is a fascinating thought that once upon a time a horse was born that turned grey and then white and the people that observed it were so fascinated that they used the horse for breeding so that the mutation could be transmitted from generation to generation," The Times Online quoted Leif Andersson, as saying. Currently, almost 1 in 10 horses carries the "greying with age" gene, which makes them brown, chestnut or black at the time of birth but their coats turn white within about six years. However, they are different from the rarer albino horses, which are white at birth. According to Samantha Brooks, a geneticist and equine expert at Cornell University, New York, the mutation in the "greying with age" gene caused the pigment cell, or melanocytes, in the hair follicles to dry up early in life.
While the hairs keep growing but in the absence of any pigment they become white and without the pigment they also become vulnerable to sunlight and thus are at a greater risk of skin cancers.
"About 75% of grey horses aged over 15 years have a benign form of melanoma that may develop into a malignant melanoma," said Andersson.
This discovery in White horses could shed light on ageing and cancer development in humans as well.
The research will be published in the latest issue of Nature Genetics.