Читать книгу Pet-Specific Care for the Veterinary Team - Группа авторов - Страница 232

With mass or individual selection, the breeder selects the animals to be bred on the basis of their superior characteristics. Whereas many breeders select their breeding stock on the basis of conformation or other physical characteristics that exemplify the breed standard, genetic counseling is intended to temper enthusiasm for physical traits with a more holistic picture of genotypic and phenotypic health (see 3.8 Genetic Counseling). Veterinarians should also exert some self‐discipline by focusing not just on one health aspect (e.g., von Willebrand status) but rather on the whole animal. Otherwise, in the zeal to rid a line of one disease, another (or more) may inadvertently be fostered.

Selection works best at eliminating dominant traits from a population. After all, because all animals that carry the dominant allele develop the trait, it is theoretically possible to eliminate a dominant trait in one generation. Selection is complicated, however, by the fact that some dominant traits (e.g., dermatofibrosis) do not appear until later in life when animals may already have been bred, and by traits with incomplete dominance or variable expressivity, in which an affected animal may not be detected yet carry the trait. Fortunately, DNA testing is now available for some of these traits, including dermatofibrosis.

With recessive traits, selection can quickly remove homozygous affected animals from breeding, but if heterozygotes cannot be detected, carriers will persist in the population. The final elimination of the trait from a breed requires identifying carriers and ensuring that no carriers are bred to one another. Even though doing so does not eliminate the deleterious allele from the population, it does ensure that no affected animals are produced.