Tag Archives: genetics

The Gene That Gives One Breed Of Cat A Curly Coat

Depending on how cat mad you are, you’ve probably never seen a Selkirk rex kitty, let alone seen or held one. They’re not a popular breed — far less than the Persian (b, in the picture above) or the Scottish fold (c) — but their main feature is a curly coat (a, left). The curly trait is dominant, so about a quarter of any Selkirk rex litter will be the less-wanted straight-hair variety (a, right).

The Selkirk rex is a very new breed, having been developed after a curly-coated (aka rex) mutation arose in a cat in 1987. There have been about 8.4 generations of these kitties, which have been outbred to British shorthairs, exotic shorthairs and Persians to establish the breed (without too much inbreeding).

Though scientists (and breeders) have known that the curly trait is dominant, they hadn’t been able to find the responsible gene. The latest — and successful — attempt comes from a team led by Barbara Gandolfi at the University of California Davis. They published their results in Scientific Reports.

The team looked at the genes of nine curly coated Selkirk rex cats and 29 control kitties, a group that included Persians, British shorthairs and straight-haired Selkirk rex cats. The cats may look different, but they all belong to a big group of related kitties known as the “Persian family.” Gandolfi’s team eventually traced the curly trait to a gene KRT71 — they’re not sure exactly what the gene does, but they know it has something to do with the development of the hair follicle (not exactly surprising).

KRT71 had been ruled out as the curly coat gene in the Selkirk rex in an earlier study that looked at curly-coated cats of several breeds, but it seems that the Selkirk rex in that study was a straight-haired cat, so the researchers would have never been able to find a curly coat gene in it. That study did find, though, that various mutations in KRT71 produced curly hair in the Devon rex breed and the naked look of the sphinx cat.

What else might mutations in this gene produce? Scientists still have a couple more curly-haired breeds to check out — the LaPerm and the American wirehair. Perhaps they’re KRT71 mutants as well.

Photos by Barbara Gandolfi, via Creative Commons license: Gandolfi, B. et al. A splice variant in KRT71 is associated with curly coat phenotype of Selkirk Rex cats. Sci. Rep. 3, 2000; DOI:10.1038/srep02000 (2013).

June 18, 2013Sarah ZielinskiPermalink Leave a comment

Tiger, Tiger, Brilliant White

White tigers, despite the name, aren’t all white. These variants of the Bengal tiger are white with black or dark brown stripes, and they also have blue eyes, pink paw pads and a pink nose. They’re not true albinos, but they’re rare. Really rare. As in, none have been seen in the wild since 1958. All the known white tigers in the world live in captivity, usually zoos.

What strips the orange stripes out of these tigers? A team of researchers led by Xiao Xu of Peking University in Beijing, reporting this week in Current Biology, examined tiger genes and found that a single amino acid change — a simple switch of one chemical piece of a protein — resulting from a mutation in the gene SLC45A2 is responsible for the white color. When a tiger has two copies of that mutated gene, it can’t produce the pigment pheomelanin that gives the cat its orange fur.

Alterations to that gene underlie similar color changes in cream-colored horses and silver chickens. The same mutation in the gene has even been found once in a human, in a German who had pale skin and dark blonde hair.

The researchers think that the mutation, which they unsurprisingly named white, evolved just once in the wild Bengal tiger population. That mutation slowly spread through the tiger’s descendents and created the occasional white tiger. The animals were spotted infrequently in India from the 1500s until 1958, when the last wild white tiger was shot. But these variants have survived in modern menageries.

White tigers are mythical, romantic creatures, which might account for why they’ve been heavily bred in some zoos, notably the Cincinnati Zoo in Ohio, in recent decades. But some have argued that white tigers should be allowed to die out. Here’s what Slate had to say in December:

On the face of it, being a white object in the Bengal tigers’ tropical habitat of India and Southeast Asia can’t be good for a predator that needs to be camouflaged. Other, more subtle problems that go along with the white coat would also prevent white tigers from ever becoming established as a wild population. The mutation (which is not albinism—white tigers can still produce melanin) also causes serious defects. White tigers in captivity tend to have problems with the way that their brains control their eyes and process visual stimulation. The animals are often cross-eyed in one or both eyes, bump into objects, and have trouble understanding spatial relationships when they are young. Animals with defects like these couldn’t survive for long in the wild, even though they have long lives in captivity. Other disorders, such as kidney problems, club feet, and shortened tendons, come from the severe inbreeding required to keep this recessive gene around.

But the new study knocks down several of these arguments. Over the years, the researchers write, many of the white tigers that were captured or killed were mature adults, so lacking the orange-and-black camouflage couldn’t have been too much of a problem. And, inbreeding — not the white mutation itself — accounts for many of the health problems that modern white tigers face, including deformities, stillbirths and premature deaths, they say.

“Despite its low frequency, this polymorphism has persisted for at least several hundred years and should be considered a part of the genetic diversity that is worth conserving,” the scientists argue in their paper.

There’s still a question, however, of whether devoting scarce conservation resources to preserving a rare variant of a creature is worth it when the entire species is threatened with extinction. There may be as few as 3,000 of these cats left in the wild. Their habitat is shrinking. And they’re being devastated by the wildlife trade. With tigers facing threats like those, perhaps a dedicated program to preserving the white mutation is little more than a luxury, even if it could be done more responsibly, with less inbreeding.

After reading the new study, I wouldn’t call white tigers “freaks,” as William Conway, former director of the New York Zoological Association, once did. And I’ll watch in amazement should I encounter one in a zoo. But I won’t be sad if the current (in)breeding programs go away and the money and resources get redirected to other conservation efforts. Because all I want is the tiger, any tiger — white, orange, Siberian, Bengal, Sumatran, et cetera — to continue to survive.

Image credit: Chimelong Safari Park, via EurekAlert

May 23, 2013Sarah ZielinskiPermalink Leave a comment

Where Did The Pigeon Get That Weird Thing On Its Head?

Visit most any city on Earth, and you’ll find flocks of pigeons. And as you stare at the birds as you sip a cup of coffee at a sidewalk cafe, you may be fascinated by their diversity: varying in color, from white to grey to black to brown. Even the common grey ones all look a little different.

But true pigeon variety is really found in the 350 or so fancy breeds that have been developed since the bird was first domesticated 5,000 years ago. (Above, clockwise from upper left: English trumpeter, Brunner pouter, fantail, Italian owl, Chinese owl, Pomeranian pouter.)

One of the traits that can make a pigeon look extraordinary is the presence of a head crest. This headgear itself can come in a variety of looks, but scientists who have sequenced the genome of Columba livia (that’s the common rock pigeon) have found that “crest” or “no crest” is determined by a single gene, called EphB2.

The trait first becomes apparent when the birds are juveniles, but the mutant gene has effects even earlier in life: When the pigeon embryo is still in the egg, the gene causes molecular changes that reverse the direction of growth of the feathers on the top of the head.

The study was published online last week by the journal Science.

Images courtesy of Mike Shapiro, Science magazine