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SELECTION AND BREEDING POLICY
(extract taken from "Genetics For Dog Breeders", second edition, 1990, author Roy Robinson F.I.Biol, Ealing, London, England)
The following page is an extract taken from "Genetics For Dog Breeders", second edition, 1990, author Roy Robinson F.I.Biol, Ealing, London, England. This is an excellent book written in very understandable language and is highly recommended reading for those interested in canine genetics. We have quoted the opening pages on breeding policy which seem a most appropriate starting point for the breeder section on these Afghan pages.
Some Preliminary Thoughts
The art and science of dog breeding rests upon two pillars of knowledge, namely selection procedures and systems of mating. In other words, the choice of certain individuals for the next generation and how these should be mated to each other. Elementary, one may say, but there are numerous ways of setting about these tasks, some of greater value than others and some of greater usefulness in solving certain problems. The two processes are complementary, but if their effects are to be appreciated, each must be considered alone in the first instance.
The phenotype of the individual iscomposed of a large number of charac- ters of varying expression. The ideal dog is one in which the expression of each character is appropriately balanced in terms of the standard of ex- cellence for the breed. This implies that intermediate grades of expression will be required for some characters but more extreme expression for others. Tne expression of genes is mainly determined by selective breeding, of which there are several kinds. The simplest is choice of the individual, but also selection can be between whole families (familial selection) or be based upon progeny testing. Reinforcing the selection are systems of mating, which embraces intense, moderate, weak or avoidance of inbreeding, the mating of like-to-like and the process of grading-up to improve inferior animals. These aspects are summarized by the diagram of Fig. 19. These are the tools which the breeder may use at his discretion.
Selective breeding is of considerable potency, whether this be straighfor- ward selection or be one of the more sophisticated forms. One has only to survey the evolution and prolification of breeds of dogs over the last 100 years to appreciate this fact. Not only have many new breeds made an appearance, but the quality of almost all breeds has improved. Despite the efficacy of selection, this alone is insufficient. The different breeds must breed true to type to be worthy of the name. It might be imagined that the selective breeding is responsible, but it is doubtful if this is true in other than a very limited extent.
The degree of pure breeding is known as the "homozygosity". The homo- zygosity varies from zero to near zero (for example, in the mongrel pups from a cross between two breeds) to near 100 per cent for a highly inbred strain of pedigree dogs. It will be appreciated that it is virtually impossible to create 100 per cent homozygotic dogs, but any value over 80 or 90 per cent may be looked upon as being highly inbred. The converse to homozy- gosity is "heterozygosity", the proportion of impureness in an individual or breed. It is often more convenient to speak of the proportion of heterozy- gosity than the homozygosity.
Selection by itself is not very effective in bringing about a high degree of homozygosity. Inbreeding is much more consistent. Not necessarily close inbreeding, but the moderate form which results from mating of not too distantly related animals. Some inbreeding is certainly desirable, if not essential, during the formation of a breed in order that the breed character- istics should stabilize around a deflnite type. Those individual dogs which deviate too much from the ideal are either not bred from or are mated to a typical specimen of the breed. In general, a breed stabilizes itself and moves forward as an entity because the majority of animals tend to be descended from, or are bred to, a small group of elite individuals com- monly regarded as the most outstanding. It is not uncommon for the elite group to be more interrelated than the ordinary members of the breed. In summary breeders who have worked to produce the top-flight animals are exceedingly choosy in their mating, and hard-won experience has taught them the inadvisability of straying too far from the basic blood-lines of the breed.
end quote @Roy Robinson