Allelic modulation in Paramecium aurelia heterozygotes. Study of G serotypes in syngen 1

Summary The systematic study of heterozygotes for the g locus controlling G serotype in Paramecium aurelia syngen 1, shows that a phenomenon of allelic exclusion exists. This phenomenon of exclusion happens either systematically, almost systematically or randomly, depending on the studied combination of alleles (Table 2). For a given combination of alleles, it is always the same allele which is excluded. Back-cross experiments indicate that the observed allelic modulation is not dependent upon a simple or classical type of regulatory system. It seems to be characteristic of a given allelic interaction.This phenomenon of allelic exclusion resembles the well-known phenomenon of mutual exclusion occurring between different loci which govern the surface antigens corresponding to the different serotypes of Paramecium aurelia. Both cases of exclusion (inter-allelic or intergenic) might involve an original mechanism of inter-regulation between proteins belonging to the same molecular family and fulfilling similar functions but under different physiological conditions.