F1Hybrids

These are the first-generation cross between two inbred strains, and being isogenic, they have many of the more useful properties of the parental inbred strains. They also usually exhibit hybrid vigor, which means that they are more vigorous than inbred strains and are less influenced by adverse environmental conditions. As a result, they tend to be slightly more uniform than inbred strains.39 However, they may also be less responsive to experimental treatments, so the increased uniformity does not necessarily mean that fewer animals are needed to attain a given level of statistical precision in an experiment. F1 hybrids are heterozygous at all the loci at which the parental strains differ, so they will not breed true. Mating two F1 hybrids gives an F2 hybrid, which is a genetically segregating generation. F2 hybrids are widely used for genetic mapping studies but are of less value as general research animals.

Designation of F1 Hybrids

F1 hybrids are designated by giving the strain of the female parent first and the male parent second, with "F1" being appended. Thus, SJLDBA/2F1 would be the offspring of a female SJL and a male DBA/2 mouse. The strain designations are often abbreviated so that B6D2F1 is the offspring of a C57BL/6 female and a DBA/2 male.

Research Uses of F1 Hybrids

F1 hybrids have one great advantage over pure inbred strains; they are much more robust. They tend to live longer, have fewer of the idiosyncrasies of the parental strains, and are less sensitive to adverse environmental conditions than inbred strains. They are particularly valuable as foster mothers in the production of transgenic strains. However, they should be used with caution in experiments involving breeding, as their offspring will be genetically segregating for the gene loci, which differ in the parental strains. Sometimes, they also have useful characteristics not normally found in the parental strains. For example, the NZBNZWF1 is widely studied as a model of autoimmune systemic lupus erythematosus, which is not found in the parental strains.39 They can be of some value in immunological studies, as they will accept tissue, organ, tumor, or cell grafts from either of the parental strains without immuno-logical rejection. One possible disadvantage of F1 hybrids is that they tend to be intermediate in phenotype, somewhere between the two parental strains. Thus, if an experiment requires several animals differing in their phenotypes, it is better to use several inbred strains rather than several F1 hybrids.

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