Mutant Bully Whippets
The New York Times reports that testing of racing whippets has revealed the causal agent for "bully-whippets" which are so morphologically different than their dams and sires. It seems that by crossing the fastest whippet with the fastest whippet, a breeder can "double down" on a defective myostatin gene. A single copy of this gene makes for the fastest whippets at the track or in the field, while a double dose of the gene (a full pair) and you get a heavy-bodied and thick-headed dog that looks like a very ugly labrador cross.
For more on the limits of breeding "the best to the best" -- and why that is no longer done ad infinitum with cattle, see >> Inbred Thinking