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The Diversity Of Dogs

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birdie1971 | 02:53 Sun 20th Jan 2013 | Science
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According to modern science, all domesticated dogs (Canis lupus familiaris) are genetically related to grey wolves (Canis lupus). If this is correct, how can the sizes of dogs be so diverse? From Great Danes to Shih Tzus, the size difference is unlike anything else in the animal kingdom. I've tried to get to the bottom of this but every time I look the answer is always 'selective breeding'. I find this answer unsatisfactory since to my knowledge there aren't any tiny wolves or massive ones either. In short, how do you take a wolf and through 'selective breeding' create a Shih Tzus in 15,000 years?
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Few of our present breeds are more than 200 years old. Given a few thousand years we could produce our various useful types of dog.You can breed to produce whatever characteristics genetics will allow. That incudes size: the original poodle, the Standard Poodle, is taller than the Miniature Poodle and very much taller animal than the Toy Poodle. Toy poodles were only first bred in the 1950s. It includes coat. The Chinese Crested exists in two forms; one effectively hairless, one with hair; there are wire-haired Dachshunds and smooth coated Dachshunds. And the same applies to characteristics of mind, of body shape, of sight, of smell, and so on

To turn a wolf into a domestic dog doesn't take long. It took Russian biologists just six generations of selective breeding to produce a tractable, friendly, domestic dog (which looked distinctly wolf-like, as some modern breeds rather do). They could do it to produce the opposite too, an animal that would attack anyone or anything on sight. You can do a lot in quite a short time by inbreeding the animals and breeding to a desired type.
All animals can be reduced in size amazingly quickly. Take two of the smallest ones and mate, then the smallest progeny to the smallest available ect etc. Making them bigger takes a lot more generations as the skeletal structure does not increase in strength to support the weight that quickly.

In theory four young of one mating will produce one bigger, one smaller, and two the same size.
But how does a wolf turn into a mastiff? The whole profile is different.
Not all breeds of dog have been bred by man directly from the wolf. Other naturally occurring dog breeds were around as well but all genetically related to the wolf.
To complicate matters, it appears that there is a "missing link" When man first started to live in one place and farm, for the first time ever, there were rubbish heaps FULL of nourishment. The local canids changed in order to be able to benefit from this. They were already scavengers and omnivores to an extent and they evolved to be less wary of men and more able to chew and digest a variety of food.
There's a very intersting book called "Dogs" by Raymond Coppinger that explains this.
Wolves in nature are selected to be their natural size. A wolf the size of a poodle is not going to do well in the wild. Too big and they would need too much resources.

Wolves have a very diverse genome.
In animals, genes are paired, one of the pair inherited from the father, the other from the mother. For the purposes of this question, we can say that where the two genes are different, one is "dominant" over the over (usually the more "useful" of the two). So an embryonic wolf with one gene for normal size and another for abnormally large (or small) will grow to normal size. But the other gene, though not expressed in that wolf, may still be passed to its offspring. When a wolf has both genes causing it to grow to abnormal size, it will as beso says, be unlikely to survive to pass these genes on.
Genes for other characteristics work similarly.
So, the answer to your question is, that man has selected for the genes present, but not often expressed, in the wild wolf to create the breeds of dogs we see today. If dogs were allowed to breed freely with no interference from man (many probably would not be able to do so), the normal genes in the population would soon dominate and dogs would become "standardised" with wolf-like characteristics.
not wolflike characteristics but "scavenger canid" characteristics as described in the book that I mentioned.
brinjal, apart for size, there are also other genes that diverse slightly - this is in every living thing's makeup or evolution couldn't have occurred. Two dogs with smaller ears will have progeny with generally smaller ears etc. Characters for a hanging jowl-skin react the same.

If humans all purposely selected their partner for red hair, shortness, big nose, small ears etc. it would produce the desired effect in a surprisingly few generations.
Dogs can appear bewilderingly diverse, I would agreee- ranging in size from Pekingese to Great Dane, In temperament from the placid like the Golden Retriever to the agressive like the Pit Bull.

But it really does show the power of selective breeding, specifically selecting for desirable traits and then breeding for those traits, further exagerrating those charactistics.

Tracking mitochondrial DNA, it would appear to suggest that virtually all dogs today are descended from just 3 common female ancestors

Article from a few years ago on the BBC website.
http://news.bbc.co.uk/1/hi/sci/tech/2498669.stm

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