Wednesday 1 August 2012

Small Dogs

Small Dogs Biography
The small dog types are usually referred to as Toy Breed Types of Dogs but they are also referred to as miniature dog types. Some small dog types were also referred to as 'sleeve dogs', 'pocket size' and 'lap dogs'. Another popular name for small dog types are Teacup dogs. Breeders often use this cutesy phrase as a 'marketing term'! Canine Associations do not endorse or condone the use of any of these terms and would caution the perspective puppy buyer not to be misled by them. The size of small dog types is the result of selective breeding, it does not indicate that a particular dog breed type with an exceptional diminutive appearance is rare or special.

What do Chihuahuas, terriers and Pekingese dogs have in common, apart from their diminutive size? The answer is a mutation in a single gene.

This mutation, which lies in one of the body's master growth-regulator genes, is so widespread that it must have been present early in the history of dogs' domestication.

Elaine Ostrander at the National Human Genome Research Institute in Bethesda, Maryland, US, and colleagues surveyed genetic variants in a small region of chromosome 15 in Portuguese water dogs, a breed with an unusually broad size range. They found that smaller water dogs tended to carry one particular variant of the gene for Insulin-like growth factor 1 (IGF1), an important growth regulator. Dogs carrying the variant, or allele, for small size also had less IGF1 in their bloodstream.

When the researchers then turned to other breeds, they found the same variant in every small breed they looked at, but hardly ever in very large breeds such as St. Bernards, Irish wolfhounds, and great Danes.

"IGF1 functions a lot like the "reduce" button on a Xerox machine, where things can get increased or reduced proportionately," says Ostrander.


However, many other genes must also affect size. The small allele is also common in a few large dog breeds such as mastiffs and especially rottweilers. "The fact that you can see it in the mastiff or the rottweiler means it's not the whole story," says Ostrander. "It can be tolerated in large dogs as long as there is a constellation of other factors that overwhelm it."

Since dogs as large as great Danes and as small as terriers occur in the archaeological record more than 10,000 years ago, the small-dog variant of IGF1 must be at least that old, the researchers note.

However, the variant is not known in wolves, dogs' closest wild relatives. "Either man selected a small wolf, which doesn't exist now, or they found a small variant of dog that everybody liked," says Gordon Lark, a geneticist at the University of Utah in Salt Lake City, US, who was involved in the study.

Apart from the light it sheds on the evolutionary history of dogs, Ostrander's study also represents a big first step in understanding how a suite of genes interact to produce a complex trait such as body size. "We're really very clueless about how complex traits work," says John Fondon III at the University of Texas Southwestern Medical Center in Dallas, US, who was not involved in the study.
Small Dogs
Small Dogs
Small Dogs
Small Dogs
Small Dogs
Small Dogs
Small Dogs
Small Dogs
Small Dogs
How To Train Small Dogs : How To Teach Your Small Dog To Lie Down
REALLY Small Dog

No comments:

Post a Comment