The adage that you can't teach an old dog new tricks may have some basis in truth, or at least in DNA. It turns out that a pointer's point, a border collie's herding instinct, and several other canine characteristics may be hard-wired in dogs' genes, according to a new study. The advance could help breeders weed out diseases in man's best friend and shed light on the genetic basis of certain human disorders.
Since humans first domesticated dogs some 15,000 years ago, selective breeding has produced more than 300 breeds in a variety of sizes and behaviors. Which genes control these traits has been something of a mystery, but last year, an international team of researchers made a breakthrough when they discovered that a single gene plays a major role in regulating the size of small dogs (ScienceNOW, 5 April 2007). Now the same team, led by geneticist Paul Jones of the Waltham Centre for Pet Nutrition in Leicestershire, U.K., has combed through the DNA of dozens of dog breeds and pinned life span, and several behaviors and physical characteristics, to specific regions of canine DNA.
The researchers scanned the DNA of 148 breeds for stretches that differed by one base, areas known as single-nucleotide polymorphisms. They then matched these genetic variations with anatomical and behavioral characteristics of particular breeds. Several variations corresponded to skull shape, weight, fur length, and body length. For example, a variation in the SMAD4 gene, which controls cell growth, was linked to weight. A number of genetic variations that were tied to life span also appeared to regulate size, which makes sense because smaller dogs tend to live longer than larger dogs. Several additional variations were associated with certain behaviors, such as herding in collies and boldness in rottweilers, the researchers report in the June issue of Genetics.
It's not yet known how these genetic differences influence the identified behaviors or physical characteristics, Jones says. To get a better handle on that, his team plans to look at the DNA of mutts. Because mutts are a hodgepodge of DNA from different breeds, finding particular genetic variations that influence the same traits in these dogs will provide more concrete evidence of their effects.
Mikko Koskinen, a geneticist at the University of Helsinki in Finland, says the findings are a good starting place for understanding the genetic basis of dog traits. And they could ultimately help breeders choose dogs for mating that won't produce negative traits, such as timidity--or even certain diseases that may be tied to particular genetic variations--in their offspring. But Koskinen cautions that many canine behaviors are likely to be too complex to pin to a few genetic variations. That's because such behaviors are generally due to many different genes as well as their interactions with other genes and the environment.
Anita Oberbauer, an animal physiologist at the University of California, Davis, says the research could lead to a better understanding of the genetic basis of human diseases. Many of the DNA regions identified in this study are found in people, she notes, and play a role in key neurological and development processes in the body. So knowing how these genes impact certain behaviors or anatomy could shed some light on the role they play in disease. Indeed, Jones notes that several variations identified in the study reside in or near genes that have already been tied to human disorders. A gene linked to herding behavior has been implicated in schizophrenia, for example.