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PubMed1982

Both genetic background and environmental factors modify the phenotypic expression of H-2 associated genes participating in the polygenic control of antibody responsiveness to Salmonella antigens.

The genetic control of responsiveness to flagellar (f) and somatic (s) antigens of Salmonellae was studied in high (H) and low (L) lines of mice selected for the character 'antibody response to sheep erythrocytes'. The minimal immunogenic dose was, for the two antigens, lower in H than in L mice and the dominance of the responder phenotype was then greater in F1 hybrid females than in males. Genes associated with H-2 locus intervene in the responses to each antigen. Their expression was found to vary according to the conditions of immunization and to the sex. The quantifiable H-2 effect was measured in interline hybrids, i.e. on an heterogeneous genetic background equivalent to that of F2. In the case of the flagellar (f) antigen, the H-2 locus was responsible in secondary response for about 50% of the interline difference in the two sexes. In the primary response, the H-2 effect was only observed in females. It was smaller (25% of the interline difference) and independent of the antigen dose. In contrast, with somatic (s) antigen the H-2 locus did not intervene in the control of secondary response. The H-2 effect in the primary response was again only found in females. Unexpectedly, the allele linked to the H-2 phenotype of L mice had a more favourable effect on hybrid responsiveness than that linked to the phenotype of H mice.

Animals↗
PubMed1993

Effects of environmental changes on natural selection active on human polygenic traits.

During the last century, industrialized countries experienced such an improvement in socioeconomic conditions and in sanitation that it is likely that the selective forces active on human metric traits have been modified. Perinatal mortality as a function of birth weight is one of the clearest examples of natural selection in humans. Here, trends over time of stabilizing and directional selection associated with birth weight have been analyzed in Japan from 1969 to 1989. The population of newborns has been subdivided according to gestational age, which is one of the main covariates of birth weight. The results show that in full-term babies both stabilizing and directional selection are coming to an end, whereas in babies born after 8 months of gestation these selective forces are still active, even if at much lower levels than in the past. The peculiar results found in the 7-month-gestation population are probably due to grossly abnormal cases of immaturity.

Birth Weight↗