Dr Liesel van der Merwe is a small animal medicine specialist. Send her your questions: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Dr Liesel van der Merwe

Let’s discuss the pros and cons of selecting pure-bred versus random-bred dogs.

A litter of puppies from an unplanned mating may have more than one father, thus the determination of parentage in many dogs is virtually impossible. Predicting the dog’s appearance and personality is more of a lucky dip.

However, mongrels have some advantages to their purebred cousins. It is not a guarantee that they will not have genetic problems or diseases, but the chances are less. As a group, dogs of varied ancestry will be healthier than purebred dogs because the gene pool is expanded and more diverse, with a decreased likelihood of two recessive genes being present to express as a physical condition.

Everyone has a set of chromosomes, each containing two halves, one from each parent. Each chromosome is made up of genes which link up in pairs to create a double helix. Groups of genes carry all the body’s information.

The ‘dominant’ gene is the one that is expressed, such as for brown eyes. A ‘recessive’ gene produces a particular trait, such as blue eyes, only if its effects are not over-ridden by those of a dominant gene. Both genes have to be of the recessive type for a recessive characteristic to be expressed.

Genes are normally transmitted unchanged from one generation to the next, but sometimes a mutation occurs: The structure of the gene is changed.

Today there are more than 300 dog breeds. To create specific dog breeds, individual dogs with desirable physical characteristics or traits were bred with each other. This resulted in a narrower genetic pool within a species and a huge variation between breeds.

With purebred dogs genetic variations are well documented: Labrador retrievers are predisposed to elbow and hip dysplasia; Dachshunds are predisposed to disc prolapse and spinal cord damage; huskies are predisposed to epilepsy; fox terriers are predisposed to severe skin allergies; boerboels may develop compression of the spinal cord due to neck vertebra malformation as well as dilated heart disease causing failure.

This is because current breeding practices within the pedigreed dog community result in the reduction of genetic diversity and the increasing physical expression of recessive genetic traits.

Most breed societies try to limit the continued breeding with dogs affected by recessive conditions. With the increase in understanding of genetics, an increasing number of conditions can be determined by testing the DNA of a puppy.

If you want to buy a purebred dog, make sure you understand which conditions are commonly associated with the breed. There are cost implications as well as implications to your lifestyle with many of these conditions.

Speak to the breeders and ensure that they are taking the steps established by their specific breed standards to limit the continued transmission of these defects, for example German Shepherds and Labrador retrievers need to be certified free of hip dysplasia.