A handful of genes could mark the difference between high-strung Chihuahuas and unflappable basset hounds

A comparison of 148 dog breeds has uncovered genes for size, lifespan, and even complex behaviours such as pointing and herding. Geneticists have previously uncovered genes for dog traits such as coat colour and narcolepsy, but these searches tended to focus on a single breed, comparing pooches with variations in a single trait – for example, boxers with and without white spots. This strategy does not work for rooting out the genetic basis of behaviours because certain breeds either display these behaviours or they don't, says Gordon Lark at the University of Utah in Salt Lake City, US. So with the help of a dog show judge, Lark's team scored dogs from 148 breeds for traits including herding, pointing, boldness, excitability and trainability. Then they scoured their genomes for similarities and differences. Dogs were also scored for size, body proportions and longevity. The search implicated several genes in stereotypical dog behaviours. For example, herding behaviour typical of collies and shepherds may be linked to a gene that is similar to one associated with schizophrenia in humans. Also, a gene involved in processing the neurotransmitter dopamine may explain both the boldness of rottweilers and the timidity of pugs, while a gene for brain development appears linked to pointing in dogs such as Irish setters. And though dogs both large and small showed a genetic basis for boldness, only the little dogs possess the genetic markers associated with excitability. Lark's approach worked even better for less subjective qualities, such as size and longevity. His team confirmed a smattering of genes linked with size that had been revealed by previous studies.