A Genetic Analysis of Aggressive Behavior
Materials and Methods Page 2

Title Page

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Materials and Methods
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Figures 1-3
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Tables 1-3
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Five strains of highly inbred rats were used, along with certain of their hybrids and backcrosses to be described. WAG-Rij albinos and DA agoutis were bred in the laboratory as third and fourth generation descendents of animals that had been purchased originally from Yale University Medical School. Fischer and Lewis albinos were raised in our laboratory from the litters of pregnant females which had been purchased from Charles River Laboratories. ACI Irish agoutis were raised in our laboratory from the litters of pregnant females which had been purchased from Microbiological Associates. The Fischer, Irish, and WAG-Rij lines are now over 90 generations inbred by systematic brother-sister matings, while the Lewis line is over 60 generations and the DA line over 50 generations inbred.

Although the five strains have been inbred independently for many years, the origins of the WAG-Rij and Lewis albinos are related, and the origins of the DA and Irish agoutis are also related. The WAG-Rij rats are descendents of an inbred strain originated by A.L. Bacharach in 1924 from outbred Wistar Institute stock, maintained by Glaxo laboratories, Radiological Institute of the Netherlands, and the Yale University School of Medicine in succession. The Lewis strain were also originated from outbred Wistar stock, though at a much later time (Jay, 1963). The inbreeding of the ACI Irish agouti was begun by Curtis and Dunning in 1926 (Jay, 1963). The DA agoutis were inbred by R.D. Owen beginning around 1946 from crosses among August lines obtained from Dunning (Owen, personal communication). Since the August lines and the ACI were somewhat related in their origins, one would also expect some distant relationship between the DA agoutis and the ACI Irish.

The Fl hybrid generation was obtained by reciprocal matings of the DA and WAG-Rij strains on the one hand, and the DA and Fischer strains, on the other hand. The Lewis and Irish strains were not used to generate hybrids.

The first backcross generations were obtained by breeding Fl animals with WAG-Rij and Fischer strains, respectively. Reciprocal matings were again performed in order to allow us to test for maternal differences between inbred and hybrid mothers. The resultant backcross generations will be referred to here as 2WD and 2FD respectively.

The second and subsequent backcross generations resulted from matings of inbred Fischer and WAG-Rij rats with selected animals from the previous backcross generation. The selected animals were those who showed the highest rates of offense behavior in their generation (competitive fighting in the case of females and isolation-induced fighting in the case of males).

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