Rodents (1996) / Chapter Skim
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4 GENETIC MANAGEMENT OF BREEDING COLONIES
4 GENETIC MANAGEMENT OF BREEDING COLONIES
Pages 35-43
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From page 35... ...
. Pedigrees Using a pedigree method allows the parentage of individual experimental animals to be traced; aids in selection of parental pairs to avoid the inadvertent fixation of unwanted mutations, especially mutations that would affect reproductive performance; and maximizes genetic uniformity within a strain.
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From page 36... ...
Each new mutation has a 25 percent chance of becoming fixed in an inbred strain (Bailey, 19791. The gradual accumulation of such mutations and the resulting genetic changes are called genetic drift.
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From page 37... ...
So that all animals at any time can be traced to a single ancestral pair, the number of generations of any branch other than the common ancestral branch is limited, depending on the number of animals that are produced for experimental use, the productivity or the average number of breeding pairs of progeny expected from a single mating, and the reproductive life span of breeders. Because most commonly used inbred strains today are highly inbred, breeding selection is not effective in increasing reproductive performance.
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From page 38... ...
However, pedigree management is not necessary, because there is no propagation of lines beyond that of the F1 generation. Foundation or Nucleus Colonies, Expansion Colonies, and Production Colonies In large breeding operations, it is often practical for management purposes to subdivide the breeding colony of each strain into separate groupsa foundation colony (sometimes called a nucleus colony)
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From page 39... ...
Ideally, no selection pressures should be placed on the population; however, in practice, there is often a conscious or unconscious selection for reproductive performance, and great care should be taken to eliminate this bias. Ideally, a purely random mating structure should be used so that each animal has an equal chance of participating in the breeding program and of mating with any of the animals of the opposite sex within the colony with no attention to relationship, genotype, phenotype, or any other characteristic; this requires accurate identification of individual animals, extensive record-keeping, and structured randomization in which randomization tables or computer-generated randomized numbers are used to select breeding pairs.
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From page 40... ...
In addition to the classic nongenetically defined populations maintained by random breeding or outbreeding, populations of rodents with substantial genetic diversity, as evidenced by heterozygosity at a large number of loci, can be developed by making systematic multiple inbred-strain crosses. In such a system, four or more inbred strains are regularly crossed in a circular fashion to yield F1 progeny that are systematically mated with a rotational system to provide F2 animals for use in experimental procedures.
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From page 41... ...
If a strain is preserved with scant information on its characteristics, for example, it is unlikely that it will be of much use in the future. The ILAR Committee on Preservation of Laboratory Resources has recommended the following criteria for identifying valuable laboratory animals: the importance of the disease process or physiologic function, the validity or genetic integrity of the stock, the difficulty of replacing the stock, versatility of the stock, and current use (NRC, 1990)
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From page 42... ...
In this case, it is important to identify each entry accurately according to its strain, as well as its parental and other information. For pedigree management, it is also useful to maintain a pedigree chart, at least for foundation breeders; this helps to avoid unnecessary proliferation of family branches by allowing visualization of individual animal relationships.
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From page 43... ...
Pp. 274-288 in Genetic Monitoring of Inbred Strains of Rats: A Manual on Colony Management, Basic Monitoring Techniques, and Genetic Variants of the Laboratory Rat, H
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