In natural populations of Drosophila melanogaster, two mutator systems, MR and P-M, are distributed throughout the world. Some evidence shows that these systems can be considered as one. Natural populations of D. melanogaster from Eurasia and North America are fundamentally different with regard to the P-M system. Comparison of Eurasian and North American populations with regard to the MR system was hindered by a lack of data concerning distribution and frequency of MR factors in Eurasia. In this paper, data on the MR-active chromosomes in natural populations of D. melanogaster from Russia and neighboring countries from 1977 to 1992 are presented. The frequencies of MR chromosomes in Eurasian populations were shown to be similar to those in North America. Hence, on a global scale, the MR and P-M mutator systems are expressed independently.
