In a manner of speaking, a breed’s silhouette is shorthand for its breed type. Is there any doubt about the breed of the dog below?

If it were possible to show you a line up of AKC sporting breeds by silhouette alone, the Irish Water Spaniel would be instantly recognizable not only because it is the tallest of the AKC’s spaniels, but a “bumpy” outline points to the breed’s famously crisply curled coat. But there’s one more element of that outline that is so important, it’s the source of one of the IWS’s nicknames, “Rat Tail:” A smooth coat on the tail that occurs naturally and require no clippering.

How does nature know to have curls on part of the IWS’s tail, but then taper into a smooth “rat tail” that has no curls at all?

As far as we can tell, the transition from curly to smooth hair on the tail might be the result of a complex interplay of multiple genes that control coat texture. The texture of a dog’s coat is, as we all know, influenced by several genes, and the expression of those genes can vary across different parts of the body on the same dog!  Some speculate that the gene responsible for a curly coat in breeds like Poodles and Portuguese Water Dogs could be expressed in the base of the Irish Water Spaniel’s tail, but as the tail tapers, the influence of this gene could decline and permit other genes that promote smoother hair to dominate, resulting in the “rat tail” or “whip tail”appearance.