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DNA

The material inside the nucleus of cells that carries genetic information. The scientific name for DNA is deoxyribonucleic acid, the strands of life...

You may have read my history pages, showing the evolution of the dog, showing its decedents over millions of years. Darwin suggested that wolves, coyotes, and jackals, may all have played a role, producing a complex dog ancestry that would be impossible to unravel.

Based on anatomy, most biologists have put their money on the wolf, but until recently there was little hard evidence, just lots of opinions.

The issue was finally settled in 1997 by an international team of scientists to sort out the evolutionary the family dog, they used techniques of molecular biology to compare the genes of dogs with those of wolves, coyotes and jackals.

Blood, tissue, hair from 140 dogs, 67 breeds, 162 wolves from North America, Europe, Asia, and Arabia. From each sample they extracted DNA from tiny organelles within cells called mitochondria.

While the chromosome DNA of an animal cell derives from both parents, the mitochondrial DNA comes entirely from the mother. Mitochondrial DNA will show a line of descent, female to female to female. As changes called mutations occur due to copying mistakes or DNA damage, the mitochondrial DNA of two diverging lines becomes more and more different.

Ancestors can be clearly identified when you are studying mitochondrial DNA, because clusters of mutations are not shuffled into new combinations like the genes on chromosomes are. They remain together as a particular sequence, a signature of that line of descent.

When they looked at canine mitochondrial DNA samples, they found that wolves and coyotes differ by about 6% in their mitochondrial DNA, while wolves and dogs differ by only 1%. Already it looked like the wolf was the ancestor of our pet dogs.

They then focused their attention on one small portion of the mitochondrial DNA called the control region, because it was known to vary a lot among mammals. Among the 67 breeds of dogs, they tested, they found a total of 26 different sequences in the control region, each differing from the others at one or a few sites.

No one breed had a characteristic sequence, the breeds of dogs share a common pool of genetic diversity. Wolves had 27 different sequences in the control region, none of them exactly the same as any dog sequence, but all very similar to the dog sequences, differing from them at most at 12 sites along the DNA, and usually fewer.

Coyote and jackal were a lot more different from dogs than wolves were. Every coyote and jackal sequence differed from any dog sequence by at least 20 sites, and many by far more.

Using statistical methods to compare the relative similarity of the sequences, they found that all the dog sequences fell into four distinct groups. The largest, containing 19 of the 26 sequences and representing 3/4 of modern dogs, resulted from a single female wolf lineage.

Conclusion

The domesticated dog descended from the wolf :)

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