New varieties of dogs, such as the 'cockapoo' and 'Labradoodle', seem to be the celebrity pets du jour. How did these 'designer dogs' become the talk of Hollywood?

Designer dogs, more accurately hybrid dogs, are deliberately bred mutts and generally the result of crossbreeding two purebreds. The term designer dog is used by breeders to make them sound more fashionable. Pooches that come with a 'designer' label often cost thousands of US dollars from speciality breeders, sums that are eagerly coughed up by Hollywood stars such as Jessica Simpson, Jake Gyllenhaal and Sylvester Stallone.

Many of the popular combinations are poodle crosses because people want the intelligence and hypoallergenic qualities of the poodle but without the high-maintenance temperament and yappiness. Poodles can be crossed with almost any other dog breed since they come in a range of sizes. The non-poodle parent is often chosen for its looks and/or sturdier nerves, creating mixes such as the 'cockapoo' (cocker spaniel crossed with poodle), 'Yorkipoo' (Yorkshire terrier and poodle) and the 'Labradoodle' (Labrador retriever and poodle). Another popular mix is the 'puggle', the offspring of a pug and a beagle.

Designer breeds can be healthier animals than purebreds because they draw on a larger gene pool. Genetic diversity decreases the likelihood of two dogs sharing the same inherited weakness, which are then passed on to their puppies. Indeed, some of the best-loved purebreds today were hybrid dogs in the past. Captain Max von Stephanitz is credited with developing the modern German shepherd, for example, in the late 19th century. He sought to create an all-purpose working dog and set up extensive trials with various breeds.

Another designer dog that has plenty of fans is the Rhodesian ridgeback. This dog was developed in South Africa to hunt lions. They are brave, intelligent and robust, and were probably bred from mastiffs, Great Danes, deerhounds and bloodhounds. This hybrid dog has gone on to become an internationally recognised breed, and is eligible for competitive dog shows.

Who can say the 'Labradoodle' will not one day be a Crufts champion?

Unfortunately, creating a designer dog breed is not as easy as picking two dogs and locking them in a room with some romantic music playing. Choosing the wrong breeds to cross can result in a dog that is plagued by health problems.