The Concept of Allelic Exclusion, Its Phenomenology

In the previous chapters the various degrees of phenotypic expression of maternal and paternal biochemical traits were discussed. However, extreme cases are known when one of the parental characteristics is not expressed at all. Such an extreme case of differential gene expression is allelic exclusion. In this case, one of the homologous alleles is inactivated and does not participate in the function of the gene. 

Allotypic exclusion of Ig was indirectly demonstrated when patients with polymyeloma were inspected (Harboe et al., 1962 Martensson, 1963 Martensson and Kunkel, 1965 Cohn, 1967). It was demonstrated that in heterozygotes the heavy chains of myelomic proteins have only one allotype, whereas in the blood of the same individuals both allotypes are present (Table 21). 

Analogous data were demonstrated for light chains (Harboe et al., 1962). Direct evidence of allelic exclusion was demonstrated in the example of immunoglob- 

Allotypic localization in the cell was analyzed in a number of experiments in the lymphoid tissue of rabbits (Pernis et al., 1965). With the aid of antiserums to allotypes which are controlled by allelic genes (the combinations and Al for locus Aa Ab and Ab Ab and Ab , Ab and Ab for locus Ab were investigated) the presence of two populations of plasma cells was demonstrated. Each of these populations contained only one of the two allotypes. In general both types of cell are distributed randomly. However, there were fields which showed the predominance of one of them. 

This coincidence satisfied the hypothesis that the number of molecules of different allotypes is dependent upon the number of cells which synthesize these allotypes rather than the rate of molecule synthesis within the cell (Pernis et al., 1965 see review Baranov arni Korochkin, 1973). 

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