Today, we will continue making some more general remarks on the matter of breeding companion animals. Although it is more directed to so-called breeders who often actually mate dogs to make dollars, the advice contained in today’s column is valid for the family that wishes to acquire pets and experience the processes of reproduction and birth. The fact that some beautiful puppies can emerge from a sensible mating regime is a meaningful bonus.
Breeding is subject to the chance of combination of genes. The smallest combination of genes which can determine a hereditary trait is a pair. One gene is inherited from each parent. When two genes combine, the dominant gene is the one that determines the trait. A recessive gene does not determine a trait unless it is combined with another recessive gene. Other combinations may be additive – that is, both genes contribute in part to the expression of the trait. Unfortunately, most traits that breeders are interested in are determined by a great many genetic pairs – which is why dog breeding is an art and not an exact science. Since a dog has 39 pairs of chromosomes and each chromosome contains more than 25,000 genes, the genetic possibilities are almost infinite.
Many undesirable hereditary traits are expressed by recessive genes. Such a gene can be carried down through many generations of offspring, causing no problem until it is combined with a like recessive gene. This is why recessive traits cannot be eliminated in one or two generations of careful breeding.
In contrast, dominant traits are seen in the first generation of puppies. Breeders easily recognize problems caused by dominant genes. By choosing not to breed such individuals, they can eliminate those traits from their breeding programme.
For these reasons, sporadic hereditary disorders are more frequently due to recessive genes.
Undesirable hereditary traits commonly seen by dog owners:
• Undescended testicles;
• Extra toes;
• Inguinal and navel hernias;
• Abnormally short or absent tails;
• Canine hip dysplasia and elbow dysplasia;
• Malocclusion of the jaws and incorrect bite;
• Cleft palates and harelips;
• Slipping kneecaps;
• Immunity deficiencies;
• Lowered ability to respond to stress and diseases
• Quick collapse of organ function
• Congenital cataracts;
• Congenital deafness;
• Entropion and Ectropion (rolling inwards and outwards of the eyelids);
• Progressive retinal atrophy;
• Behaviour disorders such as inherited (as opposed to acquired) aggression and shyness.
When one breeds two dogs with a common ancestor, the resulting litter inherits some of the same genes from each side of the parent (i.e., from the mother and the father). The consequence may be that the expression of traits is more uniform; but, also, undesirable recessive genes may thereby give rise to serious problems such as those mentioned above.
Most of the above text has been taken from a handbook authored by Drs. Carlson and Griffin.
We have kept it short today. The subject matter is complicated and quite technical. We nevertheless hope that breeders and those who wish to acquire canine companion animals have grasped the fundamental issues relative to breeding. If not, please feel free to contact us for more (specific) information.