Re: News: DNA mutation explains huge variety in dog sizes.
- From: "Craig T" <craig.tevis@xxxxxxxxxxxxxxxxxx>
- Date: 7 Apr 2007 12:06:42 -0700
On Apr 7, 8:44 am, Ye Old One <use...@xxxxxxxxx> wrote:
DNA mutation explains huge variety in dog sizes: study
http://uk.news.yahoo.com/afp/20070405/tsc-us-science-dogs-e123fef.html
AFP - Thursday, April 5
CHICAGO (AFP) - A single genetic mutation explains why dogs vary in
size from the miniature Chihuahua to massive mastiffs, a range
unmatched by any other mammal, according to a study released Thursday.
Researchers have long puzzled over the tremendous variation in size
seen in canine breeds, particularly since the species diversified over
a relatively short period of time from an evolutionary standpoint.
The new study suggests the riddle can be explained by a combination of
a genetic accident that created a small dog and ten thousand years of
selective dog-breeding that ensured the rapid dissemination of this
particular piece of doggy DNA.
The researchers believe the discovery of the DNA mutation could also
help explain why humans vary so much in size.
"The study is a major milestone in canine genetics. We have precisely
located the major gene that produces our miniature breeds," said study
co-author Paul Jones, a genetics researcher at Mars Inc, the US
confectionery and pet food giant which supplied DNA samples used in
the study.
All told, an international team of researchers examined the DNA of
more than 3,000 dogs from 143 breeds ranging from pocket-sized pooches
such as the Chihuahua, Maltese, Pomeranian, pug and Pekinese to the
huge Great Dane, St. Bernard and Irish Wolfhound.
They found that all dogs under 20 pounds (9 kilos), and virtually all
of the small canines studied, carried minute genetic variations on the
gene IGF-1 which codes for a protein hormone called insulin-like
growth factor 1.
The IGF-1 gene's hormone helps humans and other mammals grow from
birth to adolescence. In small dogs, one or more mutations in the DNA
next to the gene suppresses its activity, keeping small dogs from
growing larger, the researchers reported in the journal Science.
The investigators found the genetic fingerprint in breeds that are
distantly related and found in distant regions, suggesting that this
hiccup in doggy DNA probably occurred about 12,000 years ago.
"It's as ancient as small dogs," said Gordon Lark, a biologist at the
University of Utah in Salt Lake City who worked on the project.
"Dogs are derived from wolves. Since this is found in all small dogs,
it either got into dogs when they were first domesticated or it was a
small wolf that dogs descended from."
Over time, and under the management of humans, the species saw a rapid
diversification into a multitude of domestic dog breeds. The
researchers believe there was a bias toward breeding small dogs
because they were easier to maintain in the crowded confines of
developing cities and villages, and more easily transportable during
trade and migration.
The findings have implications far beyond the canine world, the
authors said.
"By learning how genes control body size in dogs, we are apt to learn
something about how skeletal body size is genetically programmed in
humans," said Elaine Ostrander, a senior author of the study and chief
of cancer genetics at the National Human Genome Research Institute
(NHGRI), which is part of the National Institutes of Health.
"Nearly all of what we learn from studying body structure, behavior
and disease susceptibility in dogs helps us understand some aspect of
human health and biology."
Researchers at NHGRI led the study with help from colleagues at
several US and UK institutions including Cornell University in New
York, the University of California, Los Angeles, the University of
Southern California in Los Angeles, and the Waltham Centre for Pet
Nutrition in Leicestershire, England.
--
Bob.
LiveScience mentioned a few things I didn't see in the Yahoo story:
http://www.livescience.com/animalworld/070405_small_dogs.html
"The DNA snippet isn't actually a gene-it's called a regulatory
sequence. This sequence is next to a gene that regulates a growth-
inducing protein hormone that helps humans and other mammals grow from
birth to adolescence.
In small dogs, one or more mutations in the regulatory sequence
suppress the gene's activity, so it won't produce as much of the
hormone, Lark said, effectively preventing any Labrador-sized
Chihuahuas.
Medium and large dogs are missing this regulatory sequence, said study
team member Kevin Chase, also of the University of Utah. So Great
Danes can grow to their normal, intimidating size. Other genetic
material that has yet to be identified also likely contribute to the
size of these dogs, he added.
Oddly, Rottweilers also have the sequence, but other genetic factors
likely make them big, Chase said."
.
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