Polygenic regulation of anti body synthesis to sheep erythrocytes in the mouse: a genetic analysis
Selective breeding for the character "agglutinin production t o heterologous erythrocytes" was performed o n random-bred populations of albino mice. Two types of selection were carried out: Selection I: the first 6 generations were immunized with sheep erythrocytes (SE), then SE and pigeon erythrocytes (PE) were alternated at each generation t o avoid the interference of maternal antibody. Selection 11: all generations were immunized with SE 60-70 days after weaning in order t o eliminate the maternal antibody. Both were selected for the character agglutinin titer 14 days after immunization using an optimal dose of erythrocytes.
Selection I. The mean response t o SE of the foundation population was 7.36 k 1.60. The selection limit was attained between the 15th and the 20th generation. The Fzo -F30 were considered as homozygous for the character investigated. The mean SE agglutinin titers were 9.15 (1/2820) in the high responder line and 2 (1/20) in the low responder line. This corresponds t o 140-fold interline difference in agglutinin titers. SE agglutinins determined in F, hybrids, F, hybrids and backcrosses obtained from F23 -Fzs demonstrated incomplete dominance of high responsiveness (23-29 '%).
The inbreeding coefficient produced by close colony breeding was 0.55 in high and 0.7 1 in low responders at the 20th generation when both lines were homozygous with respect t o agglutinin synthesis.
Selection II. The mean response of the foundation population t o SE was 7.79 * 1.56. The selection limit was attained in F14-FI7generations that were considered homozygous for the character investigated. The mean SE agglutinin titer was 9.2 (1/2900) in high responders and 2.8 (1/35) in low responders, which is an 83-fold interline difference in agglutinin titers. The results of both selections indicate that the character agglutinin synthesis is subject t o polygenic regulation. The heritability (h2) of this character was estimated t o be between 0.18 and 0.36 (range between the extreme values of Selections I and 11).
The attempt t o evaluate approximately the number of "loci" is compatible with the hypothesis that a group of about 10 loci regulates the quantitative antibody response. The sources of errors of this evaluation and the significance of the term "loci" are discussed.