Re: News: DNA mutation explains huge variety in dog sizes.


"Ron O" <rokimoto@xxxxxxx> wrote in message news:1175968357.782338.258490@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Apr 7, 11:34 am, Boswell <j...@xxxxxxxxxxxx> wrote:
On Sat, 07 Apr 2007 13:44:51 GMT, 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."

Let's consider the logic of this claim. In a wolf pack the offspring
are produced by a single breeding pair consisting of the alpha male
and the alpha female. Therefore - if we go with option one - we must
accept that dogs are all descended from a mighty twenty pound wolf who
fought his or her way to the top of the pack. Somehow this seems a bit
doubtful. So, what about option two? Several tens of thousands of
years ago, hunter-gatherers were raising Pomeranians?



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.- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

The mutation is likely recessive if mice are anything to go by. It
might have been segregating in the population of domesitic dogs, but
there were probably several domestication events. This doesn't have
to be an ancient mutation. To make that claim they need more
information about the sequence surrounding the gene. They need some
idea of whether it has occurred more than once and if only once how
much of the surrounding genome is still in linkage disequalibrium with
the mutation. The less similarity around the gene the longer it has
been in the population and recombined with other haplotypes. There is
a limit, but there were likely rapid selection sweeps for this gene as
it was placed in various breeds and rapidly fixed through inbreeding.

This gene could have rapidly spread throughout the world in just the
last couple thousand years. There isn't much more portable trade item
as a small dog and the 25 pounders could easily feed a family for
several days.

We should wait for the paper and see what they have done so far.

Oh, the paper is out:
http://www.sciencemag.org/cgi/content/short/316/5821/112

I don't have access to the article, but the abstract mentions a
'selective sweep' - presumably in the small breeds.

--------------------------------
A Single IGF1 Allele Is a Major Determinant of Small Size in Dogs
[snip names and affiliations of 22 authors]

Abstract:
The domestic dog exhibits greater diversity in body size than any
other terrestrial vertebrate. We used a strategy that exploits the
breed structure of dogs to investigate the genetic basis of size.
First, through a genome-wide scan, we identified a major quantitative
trait locus (QTL) on chromosome 15 influencing size variation within
a single breed. Second, we examined genetic variation in the 15-megabase
interval surrounding the QTL in small and giant breeds and found marked
evidence for a selective sweep spanning a single gene (IGF1), encoding
insulin-like growth factor 1. A single IGF1 single-nucleotide
polymorphism haplotype is common to all small breeds and nearly absent
from giant breeds, suggesting that the same causal sequence variant is
a major contributor to body size in all small dogs.
--------------------------------

I haven't read the article, but just from the abstract, it is pretty
clear that they have nailed it. A very nice and very simple result.
It is the kind of thing that will probably appear as an example in
high school biology textbooks a few years from now.

But what this posting is really about are some meta-issues. Like, how
come we are just learning this simple fact now. And how come it took
collaboration by 22 people to discover it. And whether the ToE was
involved in this research in any way.

I'm not going to say much about these issues now - I am simply inviting
comments from all segments of the t.o. community. I'm just going to
point out some of the technical terms appearing in the abstract - things
like "QTL", "selective sweep", "chromosome 15" (actually just the fact that
dog chromosomes have identifying numbers), "insulin-like growth factor 1",
"haplotype", and "single nucleotide polymorphism". You can learn the meanings
of these technical terms by Googling, if you don't know them already. But
you should also contemplate the sheer volume of research and education which
took place just so that those 22 authors and their target audience would be
already familiar with those terms and would know how to make use of them
in discovering why small dogs are small.

But there is another meta-issue which arises. There has been a lot of
speculation in this group about "genes for religion" and the like. Given
the effort which was required to find a gene for size in dogs, is it
likely that genes for religion in humans will be identified by researchers
any time soon? Or genes for intelligence? The frightening spectre that a
truly informed kind of eugenics will appear within my lifetime seems unlikely
to me. But then, research that takes 22 co-authors today may be something
appropriate for a high-school science project a generation from now. Who
knows?


.

Relevant Pages

  • Re: HOW SAD
    ... Please check the basics of color genetics first. ... are not deaf because they are not "true white" dogs. ... on their coats and their phaoemelanin (yellow pigment) is so ... these "white" breeds have pale cream or off-white phaomelanin pigment. ...
    (rec.pets.dogs.breeds)
  • Re: News: Stubby legs of dachshunds, corgis, stem from single altered
    ... other breeds stem from the mutation of a single gene early in the ... evolution of domestic dogs, a study published Thursday has found. ... mutation is a retrotransposed gene. ... that same one gene variant. ...
    (talk.origins)
  • Re: the one-dog two-dog dilemma
    ... I absolutely believe that dogs have a wide range of emotions, ... For example, I just bought new muzzles, because Gene ... one for Stan, to match his collar, and a royal blue one for Gene, to ...
    (rec.pets.dogs.behavior)
  • Re: News: DNA mutation explains huge variety in dog sizes.
    ... seen in canine breeds, particularly since the species diversified over ... located the major gene that produces our miniature breeds," said study ... In small dogs, one or more mutations in the DNA ... 'selective sweep' - presumably in the small breeds. ...
    (talk.origins)
  • Re: News: Gene fragment controls size in dogs
    ... Scientists have just discovered which gene fragment controls the size of dogs, the mammal with the greatest range in size: no other species produces adults with 100-fold differences, like that between a 2-pound Chihuahua and a 200-pound Newfoundland. ... researchers analyzed 3,241 purebreds from 143 breeds. ...
    (rec.pets.dogs.behavior)
Loading