There are many hundreds of registered dog breeds and selecting a new puppy can be a daunting task when faced with such a choice. In general the breeds within each group share a similar working or functional origin, but usually that working role is redundant. Individual breeds display 'breed specific' behaviour and traits (such as reactivity) that affect their suitability for domestic life. These behavioural traits are very important when choosing a puppy.
Breed specific behaviour has been produced by selectively breeding dogs that have an increased motivation or tendency to perform a particular behaviour such as guarding, holding things in the mouth, pointing or herding. These behaviours are a natural part of the dog's normal repertoire. Some of these breed specific behaviours, eg herding, can become misdirected (dogs that herd strangers away and nip at them).
In addition to the desirable qualities shown by pure bred dogs there can be some negative health issues associated with pedigree dogs. Over many years of selective breeding some significant inherited health issues have become fixed in certain breeds. Many of the dogs with short noses such as bulldogs, and pugs now have problems breathing, and almost all cavalier King Charles spaniels have a malformation of the brain (syringomyelia) which can cause marked clinical signs. The British Veterinary Association and the Kennel Club are working together to try to reduce the levels of some diseases in certain breeds and breed related health schemes are available to screen for elbow dysplasia, hip dysplasia, syringomyelia and a number of eye diseases. In addition there are many tests available for genetic diseases. If you have any concerns about your dog's health or are considering buying a pedigree puppy then contact your vet for advice on what specific problems to look out for.