[b_sharp]

"So just where did canines and cats diverge? Besides, they have a different number of chromosomes"

Dogs have 78 chromosomes, far more than humans and more than any other diploid organism. The massive increase in information in the dog genome is due to the mechanism of selection, artificially accelerated by man**. Without the selection by man, the differences between the genomes of cats and dogs would be far less.

**Note the importance is in the mechanism and not the 'who' of the selecting, any selection at all whether natural, sexual, kin, or human selection would accomplish the same changes, albeit at different speeds and possibly in a different direction. If the dog species were in the wild they would be considered a 'ring-species'.

[Ichneumon]

Dogs have 78 chromosomes, far more than humans and more than any other diploid organism. The massive increase in information in the dog genome is due to the mechanism of selection, artificially accelerated by man**. Without the selection by man, the differences between the genomes of cats and dogs would be far less.

Well... Not really.

Domestic dogs do have 78 chromosomes, but then so do other canids, including the coyote and the timer wolf. And since neither one of those are domesticated, their 78 chromosomes are not the result of artificial selection by man. Clearly, domestic dogs just inherited the pre-existing wild canid chromosome number.

And while 78 chromosomes is pretty high, it's not the largest. Tarsius syrichta (a tarsier, a kind of small primate) has 80 chromosomes, Ichthyomys pittieri (a Venezuelan semiaquatic rodent) has 92, and Tympanoctomys barrerae (the red viscacha rat) has 102.

And that's just the mammals. Lampreys (a primitive fish) have up to 178 chromosomes, depending on species. Sharks have anywhere from 70-ish to 104 (again depending on species), etc.

But don't mistake number of chromosomes for total genome size. Dogs have 78 chromosomes, compared to 46 in humans, but their total genome size is actually a bit *smaller* than the human genome. Remember that chromosomes can come in various sizes. Mammalian genomes are roughly the same size, compared to the range found in other classes:

Mammal species which have more chromosomes usually do it by having each chromosome smaller, on average. The DNA sequences are just "repackaged" in differently sized "chunks" in different species.