Selection for leukocyte counts in mice

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Abstract
By directional selection for total leukocyte counts from a hybrid mouse stock we have gradually established two lines of mice, LLC (Low Leukocyte Count) and HLC (High Leukocyte Count), which differ both in total and in differential leukocyte counts. A randombred line (RLC) is also being concurrently maintained. Other variations between these lines of mice are in body weight, in the frequencies of coat color genes, reproductive performance, and resistance to X-irradiation. The LLC line was comparatively low in the latter two physiological parameters, and high in variation of body weight.Responses to selection for high and low leukocyte counts were asymmetrical. In the first two generations, responses were irregular; thereafter they were large in the low line (LLC) for two or three generations and then became small in comparison with those of the high line (HLC). At eleven generations of selection, the mean leukocyte count of HLC is about three times that of LLC Responses of the different cell types were proportional to their individual percentages of the total counts. There were sexual differences in the counts of total and individual cell types. Selection for total leukocyte counts affected the proportions of the individual cell types. Heritability estimates based on selection differential and response and on sib relationships yielded values ranging from 0·15 to 0·39.