Category Archives: Genetics & Heredity

Genetics and the Dog: Breed Action

In some breeds, admitting to the occurrence of an inherited defect is hazardous. Many breeders will openly condemn those who confess to having had a problem. It is as if breeders believe that silence will make the defect go away. This is clearly not the case, indeed, it is more likely that defects will spread. It is far more mature to admit to problems and collectively try to solve them. In the short term there may be heartache and economic loss for some, but in the long term the breed will benefit. It is crucial that breeders do not simply rely on pedigree data vvhen trying to evaluate problems. If a defect is recessive or suspected as being recessive, then the need is not only for five generation pedigrees of affected animals but also numbers of the litter born, their sexes status and, in the case of defects seen in later life, the age at examination. Given such data, a geneticist can help a breed examine the problem in depth. Given a list of “affected” pedigrees only on is in danger of “tracing the defect to a certain dog” without being aware that all pedigrees, affected and normal, trace to him. Any widely used stud might appear in “affected” pedigree without actually being the source of the problem though in some Read more […]

Genetics and the Dog: Test Mating

Test mating dogs for recessive defects is often rnooted and it can be effective in certain instances. Table 2 The percentage error in test mating as A? animal to as or Aa mates Number of normal pups born Percentage error when mating to affected (aa) mate Percentage error when mating to carriers (Aa) mate 1 50 75 2 25 56 3 12.5 42 4 6.3 32 5 3.1 24 6 1.6 18 7 0.8 13 8 0.4 10 9 0.2 7.5 10 0.1 5.6 11 0.05 4.2 12 0.03 3.2 13 0.015 2.4 14 – 1.8 15 – 1.3 16 – 1.0 (Figures in body of table shows percentage error if only normal pups result and one assumes tested dogs ot be AA) TABLE 2 shows the consequences of mating to affected animals and to carrier animals. In each case, one’s normal male (or female) is mated to the aa or Aa case and one looks for affected (aa) progeny. The appearance of just one affected animal proves that the animal an test was actually Aa and therefore a carrier. If, however, no affected offspring occur, can we assume the dog to be free of the gene? The answer is yes, but only with various level’s of risk. In their battle with PRA, the Irish Setter breeders tested by mating A? dogs to aa bitches. Such a mating would give rise to 50% affected pups if the A? was Read more […]

Genetics and the Dog: Elimination of Genetic Defects

Most breeders would like to think that they could eliminate/ eradicate a defect. Generally this is not feasible. If we are faced with a dominant gene like VWD we could on testing dogs, cull from breeding all those with the condition and thus eliminate the gene in one generation. For this reason, few defects in the dog are dominant as they have long been eliminated. With a recessive gene, we only identify it when the affected animal crops up. If we take this as being aa, then we can show that both normal parents were actually Aa. Discarding the affected animal helps but discarding the parents helps more so. Unfortunately, as vve discard more Aa and aa animals, we find fewer and fewer cropping up. Many Aa animals are mated to AA stock and thus produce only AA and Aa offspring but no aa cases. We thus keep the “a” allele hidden in the population and make aa cases rarer, but they can still crop up, often after long years of apparent freedom. A recessive allele cannot be eliminated unless a technique exists which enables identification of Aa types from AA animals. Frequently this is not possible. One identifies an Aa animal only vvhen it produces aa offspring. Combating a recessive defect usually entails trying to establish Read more […]

Genetics and the Dog: Genes and defects

Dogs, like wolves from which they probably descend, have thirty nine pairs of Chromosomes. These are long thread-like structures found in each body cell and along the length of which are the genes. The number of chromosomes is fully documented but the number of genes quite unknown and likely to remain so in the foreseeable future. There are, however, likely to be many thousands and each one will influence a specific aspect of the dog or, in some instances, more then one aspect. A gene is found at a particular location on a particular chromosome and, as such it will influence a particular trait, Because a dog has two of each chromosome, one from the father and one from the mother, it has two of each gene. If the tvvo are identical, the genes are said to be homozygous and if they differ, they are said to be heterozygous for that trait. Two versions of a particular gene are called alleles. Thus we have the gene causing black pigment which comes in two versions One, designated B, causes black pigment to form in the dog while the alternative, b, prevents black pigment forming and instead leads to liver or chocolate pigment. The upper-case letter indicates a dominant allele vvhile the lower-case letter indicates a recessive. Read more […]

Genetics and the Dog: Selection for Particular Traits

There is some evidence that withers height and body weight are quite highly inherited and that they would tend to be related. We have data from GSD’s showing that sixty-day weight in the breed is about 45% heritable and thus vveights at other ages would be connected, while the genes which influence weight will also tend to influence height. In a breed seeking to increase height, progress should be reasonably rapid by the use of the taller animals in the breed. At the same time, body vveight would tend to be increased (whether one wanted this or not) and other related features would happen. Increased size vvould bring with it a more rapid growth rate and possibly increased risk of hip dysplasia. It would probably increase susceptibility of the long bones to diseases like panosteosis and it might lead to reduced hind angulation. There is also some evidence that increases in withers height are associated with greater litter size, at least up to a certain point. In breeds which are physically small, the associated low litter size has both economic and genetic drawbacks but there is minimal scope for increasing skeletal size beyond the odd centimetre or two. In general, most breeders are content to select to remain within Read more […]

Genetics and the Dog: Inheritance

When we come to look at specific structural features, it has to be admitted that the information available on canine inheritance is very much less than that available on a species such as cattle. There are numerous scientific papers, some covering half a million cattle examining the inheritance of various type features in dairy cows and I can think of none doing the same thing for dogs. We can conclude from other species and can therefore logically apply the same conclusion to dogs that type characteristics i e. conformational aspects, are inherited in a polygenic way. Thus, head structure, shoulder placement, body proportions and most, if not all, the other features comprising conformation are under genetic control but with many genes involved in each instance. This is not particularly difficult to accept since a feature such as overall head structure obviously comprises a whole series of individual details and it would be quite impossible to expect them all to be under the control of a single gene. Of course, being under genetic control does not mean that the type of genetic control is something vve can easily select for in all cases. Evidence from other species would suggest that conformational traits tend to be Read more […]

Genetics and the Dog: Nature versus Nurture

Dog breeding lore is full of cliches like “half the pedigree goes in at the mouth” or” it is two-thirds feeding and one-third breeding”. Such adages are frequently quoted and lead to the general belief that much of the dog’s appearance is occasioned by the way in which it is fed rather than the way it is bred. We should thus start by examining such ideas. The dog shows enormous variation, more so than any other species known to man. The St Bernard and the Chihuahua are capable of breeding viable offspring together, although in their particular case a good deal of help might be needed to engineer the mating !  Such vast differences are entirely genetic and owe little or nothing to feeding. The distinctions which we see among breeds in conformational aspects such as size, coat type, colour, ear shape, tail shape, length and so on, are all differences due to differential genetic make up (except where we dock tails) and owe little to anything else. In this connection, the apparent emphasis laid upon nutrition is over-rated and excessive. A Dobermann is a different shape from a Fox Terrier because it is bred to be different and has a distinct genetic make-up or, in other words, the genes seen in one are at a different frequency Read more […]

Genetics and the Dog: Standards

Pedigree dogs are generally bred with a view to their conforming to a specific standard of physical excellence. Usually, such standards include reference to character as well as conformation and the general format has normally been to seek to describe the ideal animal in relation to the type of function expected of the breed concerned. Most breeds have been developed for specific purposes, even if most of the current dogs may get little or no opportunity to indulge in such activities. Retrieving breeds were intended to work to the gun and to actually retrieve fallen game without further damaging that game. Present day retrievers may be required to do additional tasks for the shooter as well as to perform in fields quite unrelated to that for which they were originally intended, but their original task will have influenced the standard against which they are to be judged. This is an important principle which should not be lost sight of. Most Nevvfoundlands may get little opportunity to be water dogs but they should be physically and mentally capable of doing the job if the need arose and by the same token, gundog breeds ought to be able to cope with many of the demands of the shooter even if opportunities to indulge Read more […]

The faults and defects of the breeds: Herding Dogs

Australian Cattle Dogs OCD (osteochondrities dissecans) of the hock Australian Shepherds Hip dysplasia; Dwarfism; Spina bifida Bearded Collies Hip dysplasia Belgian Malinois Hip dysplasia Belgian Sheepdogs Hip dysplasia; Neoplaisa Belgian Tervurens Hip dysplasia; Thyroid disorders Border Collies OCD (osteochondrities dissecans); Hip dysplasia Bouviers des Flandres Elbow dysplasia; Hip dysplasia Briards Thyroid disorders; Hip dysplasia Cardigan Welsh Corgis Medial patella luxation Collies (Rough and Smooth) Dwarfism; Neoplasias German Shepherd Dogs Dwarfism; Panosteitis, shown as limb pain and intermittent lameness between the ages of 6 and 12 monts; Hip dysplasia; UAP (ununited anconeal process); Cartilagenous Exostosis; Pannus; Elbow dysplasia; Neoplasias; Thyroid disorders; OCD (osteochondrities dissecans); Degenerative myelopathy causes progressive hind limb paralysis in middle age to older dogs. Old English Sheepdogs Hip dysplasia; Wobblers syndrome Pembroke Welsh Corgis IVD (intervertebrate disk disease); Hip dysplasia; Swimmers syndrome Pulik Hip dysplasia Shetland Sheepdogs Hip dysplasia; Dwarfism; Thyroid disorders; Neoplasias; Muscular dystrophy Read more […]

The faults and defects of the breeds: Non-Sporting Dogs

American Eskimo Dogs Hip dysplasia Bichons Frises Patella luxation Boston Terriers Neoplasias; Patella luxation, either medial or lateral; Swimmers syndrome, the inability to stand at four to six weeks; Vertebral abnormalities Bulldogs Spina bifida, caused by ununited neural arches; Neoplausa; Swimmers syndrome, the inability to stand at four to six weeks; Hip dysplasia; Elbow dysplasia; Flaccid shoulder joints; Thyroid disorders; Vertebral abnormalites Chinese Shar-Peis Patella luxation; Hip dysplasia; Elbow dysplasia; Swollen hock syndrome Chow Chows Hip dysplasia; Elbow dysplasia Dalmatians Muscular dystrophy Finnish Spitz Patella luxation French Bulldogs Hemivertebrae, which is the asymmetric abnormal development of vertebrae, resulting in scoliosis and crowding of one half of the body, producing a wedge-shape. It often results in neonatal death or spinal cord compression in older puppies. Keeshonds Thyroid and other endocrine disorders, primary hyperparathyroidism in older dogs; Patella luxation; Hip dysplasia; Neoplasias Lhasa Apsos Patella luxation, either medial or lateral; Hip dysplasia Poodles (Miniature) Dwarfism; Hypoplasia of dens; Atypical pannus; Patella luxation; Shoulder luxation; Read more […]