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Astronomy Picture of the Day


Sunday, July 20, 2008

The mutant gene that makes horses white

White horses, such as racing’s Desert Orchid or the Lone Ranger’s Silver, are actually mutants whose defective DNA carries a gene that accelerates ageing and rapidly turns their coats grey, scientist have discovered.

Such horses would probably never have survived in the wild but for one particular white horse, born thousands of years ago, which so caught the eye of ancient humans that they protected it and did their best to breed more, according to a new study.

They were so successful that the same horse became the ancestor of almost all white horses born since. It means that Silver and Desert Orchid, which won the Cheltenham Gold Cup in 1989 and the King George IV Chase four times, were probably related.

The key finding of the researchers, at Uppsala University in Sweden, is that almost all white horses seem to carry an identical gene, implying that it originated in a single common ancestor.

White horses are unlikely to have survived in the wild. The white colouring makes them easy prey for predators, while the gene sharply raises the risk of such horses getting skin cancer. This implies 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,” said Leif Andersson, who led the study. The research will be published in Nature Genetics today.

Today about one horse in 10 carries the mutation, dubbed the “greying with age” gene. Such horses are brown, chestnut or black when they are born but their coats turn white within about six years.

They are distinct, however, from the rarer albino horses, which are white at birth.

Samantha Brooks, a geneticist and equine expert at Cornell University, New York, said the mutation in the “greying with age” gene meant that the pigment cells – or melanocytes – in the hair follicles in effect “dried up” early in life. The hairs keep growing but without any pigment they become white.

The absence of the pigment means the skin is less protected from sunlight and so is at 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.

The discovery could shed light on ageing and cancer development in humans, too. White horses appear to be going through an ultrafast version of what happens in people.

Historians believe wild horses were first tamed by humans about 10,000 years ago on the steppes of central Asia. It was probably there that the first white horse was born. Since then, white horses have become associated with legend and kingship. Pegasus, the winged horse of Greek myth, is usually depicted as a grey.

King Arthur is said to have ridden a white horse, as is William the Conqueror at the battle of Hastings in 1066.

“They have this mythical image of purity and sanctity about them,” said Brooks. “They have this innocent trait about them.”

Sonya Webster, who keeps a grey mare and a stallion at End House stud farm near Clitheroe, Lancashire, said she liked them because they stood out from the crowd. There were, however, drawbacks: “They are difficult to keep clean and more likely to get sunburnt.”

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Last year I killed a man

A central line train approaches the platform
A central line train approaches the platform. Photograph: David Levene

At 9.45am on Saturday, June 23 2007, I killed a man. A perfectly ordinary man, on a perfectly ordinary summer's day. CCTV pictures show him entering the station, unremarkable among all the passengers going to the West End. He waited at the front of the platform until he could hear my train approaching, then he calmly stepped down on to the tracks and looked directly at me as he waited for the impact.
The impact was only a matter of seconds in coming, but those seconds felt like minutes. This wasn't how it was meant to be. It wasn't how I had imagined it during my years as a Central line train driver. We talk of "jumpers"; workmates tell of blurry images flashing in front of them, of the shock of the impact. I wasn't expecting to see a young man in jeans and a summer shirt waiting for death, looking me in the eye.

As I hit the emergency brake, I was thinking, "Please, get out of the way. Now. Please let it be a prank." Youngsters on the track are a regular event, though no less frightening for that, and for train drivers it's something we learn to live with.

But this wasn't a typical game of "chicken": he wasn't laughing and he wasn't with friends. When it became clear he wasn't going to move out of the way, I closed my eyes, covered my face and held my breath.

By the time we were stationary, four of my eight cars were in the platform and I was on autopilot. I told the passengers there would be a delay in opening the doors due to an "incident", and was calling the line controller for assistance when I heard a tap on my cab door. A smart man inquired, "Do you know there's a person under your train?" I looked at the blood on the windscreen momentarily before assuring him that, yes, I was aware.

He paused for a heartbeat, looked at his watch and said, "So, how long before we get on the move again?"

I was to look back on this exchange with amusement and also, strangely, comfort: in the midst of the horror, normality was briefly restored by a commuter asking for alternative travel arrangements.

I'd advised the passengers to stay where they were and not to try to open the doors because we weren't fully in the platform; amazingly, they all complied. I walked back through the carriages opening the adjoining doors and shouting: "Please leave the train, and leave the station as quickly as possible!" Terrorist attacks were still very much on people's minds, and as each carriage emptied I looked to the next, seeing anxious faces through the windows. No one tried to leave until I opened the doors. Only a few asked the reason, none complained. I was hugely impressed.

The next few hours were a blur of activity as the body was removed and service restored: station staff, police, firefighters, the emergency support unit and trauma counsellors all came and went in a smooth, well-practised exercise. I was reassured that it wasn't my fault, that there was nothing I could have done; it was his choice. All of which I knew, but it was good to hear from someone else.

As a child of the enlightenment, a rationalist and an atheist, I was sure I wouldn't be unduly affected by the death of a person unknown. I was told I'd need some time off in case of post-traumatic stress; I agreed to counselling to assess my fitness to resume work, but was convinced this would be a formality.

My return to work was speedy and for weeks I was seemingly unaffected. But in August a policeman came to brief me before the inquest and to show me the pictures. The unknown person now had a name, a family and a tragic story.

Henrik Alexandersson had moved from Sweden to find work in London; he was successful and popular, but had been unwell. For some reason, he'd convinced himself his illness was Aids-related and that week he had gone for a check-up to find out the truth. By that Saturday, he could bear to wait no longer: he called his parents in such a state of distress that they booked a flight to London (arriving just hours too late.) He left a suicide note, and headed off for his fateful meeting with me. Had he waited a day longer, he would have learned that the tests were negative.

I left work and went home in the full realisation that perhaps I am not such a rationalist after all, because I sobbed my heart out in the arms of my partner. A year has passed now, but I can still see Henrik standing on the track, awaiting the inevitable.

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What the Hell is Going On in Potters Field?

These photos, taken from a Flickr set, show what appears to be some sort of crashed spacecraft in London's Potters Field. They offer no explanation as to what's going on over there across the pond. Do any of you know what this is? Movie shoot? Publicity stunt? Photoshoppery? Actual alien invasion? Let's hear your guesses, both educated and uneducated, in the comments. Update: It's an ad for a new car. Boo.

Potters Field Invasion

[Flickr via NotCot]

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