Studies on the individual selection for sugar beet breeding. : IV. On the application of rejection of rejection ellipsis to individual selection.

The effectiveness of the assortative mating of selected individuals in increasing selection response was tested, using abdominal chaeta score in Drosophila melanogaster. Three paired comparisons were made. In two sets of lines with 10 matings per line, individual score was used for selection and as the basis for the assortative mating. In the third set with 20 matings per line an index of individual and family score, designed to maximize rate of response, was used.The intensity of selection was one in ten in all lines. Flies were raised in vials and individual pedigrees were kept.In all comparisons, assortative mating gave a greater selection response, this being partly due to a greater realized heritability and partly to a greater selection differential. The effect of the assortative mating was largest in the index selected lines. With random mating, the effectiveness of the index selection itself when compared to individual selection was in accordance with theory.In two comparisons, assortative mating increased the rate of inbreeding. The highest rate of inbreeding was observed with index selection and assortative mating, even though there were here twice as many matings as in the individually selected lines.In the individual selection lines, the effective population size was 7·4 pairs of parents, compared to the actual value of 10 and in the index lines 7·0 compared to 20. In the former, only one-half of the matings in the initial generations made any permanent contributions to the line and in the index lines only one-third. Within generations and lines, there was a significant positive correlation between the mean score of a family and its inbreeding coefficient.It is suggested that assortative mating is a method of increasing selection response in some situations. Its particular characteristic is that it becomes more powerful when the heritability is high whereas all of the other environmental aids to individual selection are more effective when the heritability is low.

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Selection for leukocyte counts in mice

Genetics Research ◽

10.1017/s0016672300010004 ◽

1966 ◽

Vol 8 (2) ◽

pp. 125-142 ◽

Cited By ~ 6

Author(s):

C. K. Chai

Keyword(s):

Body Weight ◽

Coat Color ◽

Leukocyte Count ◽

Individual Cell ◽

Cell Types ◽

Two Generations ◽

X Irradiation ◽

Leukocyte Counts ◽

Selection For ◽

The Individual

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.

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