Posted on 12/21/2004 8:45:42 AM PST by PatrickHenry
The wide range of variety in domesticated dogs — from the petite Chihuahua to the monstrous mastiff — has powered a new view of what drives evolution.
Scientists have long known that the evolutionary changes that alter a species' appearance or create new species frequently occur in rapid bursts. One widely accepted theory holds that any evolutionary change results from a random switch of a single genetic unit within DNA.
These single-point mutations occur in about 1 out of every 100 million DNA sites each generation. This frequency is too low to cause rapid evolutionary change, assert John W. Fondon and Harold R. Garner, biochemists at the University of Texas Southwestern Medical Center at Dallas.
While examining human-genome data, Fondon found that small segments of repeated DNA sequences, called tandem repeat sequences, are frequently present in genes that control how an animal develops into its final appearance. Unlike single-point mutations, tandem repeat mutations occur when a cell's machinery for copying DNA makes a mistake and inserts a different number of sequence copies.
Such mistakes, which happen 100,000 times as often as single-point mutations, could alter an organism's appearance or function for successive generations.
"I was stunned by what I found," says Fondon. "It occurred to me that this might be a nifty way for [organisms] to evolve very rapidly."
To evaluate this hypothesis, Fondon and Garner looked for tandem repeat sequences in 92 breeds of domesticated dogs. For example, they examined a gene that determines nose length. They found that the number of times a particular sequence is repeated correlates strongly with whether a breed has a short or long muzzle.
Many researchers explain dog-breed diversity as the emergence of hidden traits in the genome. However, says Fondon, a more likely scenario is that genetic mutations occur in dogs at a high rate.
By comparing skulls of dogs over decades, Fondon and Garner found significant and swift changes in some breeds' appearances. For example, between the 1930s and today, purebred bull terriers developed longer, more down-turned noses.
Moreover, the researchers found more variation in tandem-sequence repeat lengths among dogs than they found in the DNA of wolves and coyotes.
These results suggest that dogs have experienced significantly higher rates of tandem repeat mutations than the related species have, says Fondon. Because tandem-repeat sequences litter the genes that control the developmental plan in many species, Fondon suggests that mutations in these regions could have a strong bearing on evolution.
"As a new finding about the biology and genetics of dogs, I'm all for it. But in terms of applying this to [evolution in general], I think there's a question mark," says Sean Carroll, an evolutionary geneticist at the University of Wisconsin–Madison.
Carroll notes that because dog owners have coddled their companions over the centuries, mutations that would have killed wild animals may have persisted in the gene pool of domestic dogs. Because domestication diverges from a standard model of evolution, he says, further experiments are necessary to add weight to Fondon and Garner's theory.
Do you have a source for this?
I read the assertion in the link with some interest. I note that the terminology here is different from what I heard around the farm. But what is done with this non-sterile mule mentioned therin? Who's his baby?
There's a lot of Angora goats in West Texas...I seem to remember Sam Donaldson getting a nice tax break from the little horned poodles.
My lab would play with them all unless I tossed them in the air and shot them over the water. Then she'd wait for me to signal and go get them.
Don't know. Never saw it happen myself.
Ironically, I learned that mules are not always sterile in Asimov's Foundation series --- had to go look it up, because, like you, I thought mules were always sterile.
Angora = Emu, 10 years later, IMHO.
Not that I don't raise them and sell them to people with "ranches" outside of Houston, mind you.
I don't suppose that could be due to breeding choices of the owners???
There's one not quite this bad on a route I travel--being kept as a pet, I fear, with no knowledge that they're going to have to get it shorn! I've been wondering whether to play the busybody and give them a call. Then they might expect me to find them a barber. Did you know that some wool producers now have a hormone they can inject into the sheep which will cause all the hair to fall off in a convenient fleece? I thought it would revolutionize wool production, but it is not widely used. I suspect it may harm the meat...?
Something my Biology Professor said years ago and Michael Moore does not count......
I believe, though, that they have studied populations of feral dogs, and their diversity.
Mutts do, after a few generations, tend to lose the non-dominant breed specific traits, and all tend towards the characteristics that match coyote/wolf traits.
So I would be hard pressed to say that specific breeds is a tendency in evolution. Those breeds were selectively bred for the desired trait. Evolution tends to support a more general purpose mutt.
Thanks for the ping!
The only limitation here is physical, same as with some humans, Pygmies and Zulus, comes to mind, but no one would claim that they both are not the same species. A dog in heat is a dog in heat, regardless of size, shape or demeanor. The attempt would be made by them in spite of size difference. And if successful would produce viable reproductive offspring....
Heh, heh...
If I am not mistaken, it was Cokie Roberts who said recently that Michael Moore hurt the democratic ticket (paraphrasing, probably erroneously)..."just by his physical appearance."
I have two GP Mutts and two pure breds, Retriever and Chihuahua. My GP mutts are smarter and easier to train. The pure bred Retriever just wants to play fetch, which is what he was created for. The Chihuahua just wants to be petted and lay around all day, for the same reason....
Not handy, but you can Google "humanzee" or various combinations of "hybrid" or "chimera" and come up with it pretty easily.
Also, nutcase biologist Newman (?) filed a patent on human-chimp cross in the US, I think.
Interesting, but terribly disturbing.
> What's a Poofist?
A more accurate description of the fariy-tale of Creationism. God said "Ummm..." and all the critters of the world went "poof" and there they were. The fossils went "poof" and there they were, already made, and made old, showign clearly evidence of evolution (God apparently playign a little prank). The stars and galaxies went "poof" and there they were, billions of lightyears apart, but wioth the light already travelled between.
Yes, it's silly... but that's Poofism for you.
> Darwinism really has taken on the mentality of the Left.
Somehow, you misspelled "Creationism" as "Darwinism."
My girl ridgeback is a ridgeless as well, she was the sweetest dog of the litter, and without the ridge she was a good 700 dollars than the good dogs with ridges. There is a great breeder of champion ridgebacks 10 minutes away from me in OK, that is where I got her. If you are ever in the market for a ridgeback again, I would be glad to put you in touch with the breeder.
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