Abstract
The high level of inversion polymorphism and, correspondingly, the abundance of inversion banding sequences (BSs) of polytene chromosomes in the banding sequence pool of Chironomus species permit scientists to reconstruct the cytogenetic evolution of the genus and to evaluate the role of structural rearrangements in the genome during population divergence and speciation. We performed a quantitative assessment of the important role of inversion polymorphism in the differentiation of natural populations and demonstrated the adaptive significance of different gene orders in populations of species occurring in different regions. For the first time, it has been shown that the BS pools of populations of the same species on different continents differed much in the sets and frequencies of gene inversion orders. BS pools of populations on each continent were found to contain continent-specific BSs in addition to sequences occurring on several continents. This intraspecies diversity of the linear organization of the genome is one of the major factors maintaining the evolutionary stability of species in dramatically different environments. In addition to endemic species-specific sequences, the BS pool of the genus Chironomus contains sequences common for different species, cytocomplexes, and continents. These sequences, termed basic sequences, are very important for reconstruction of genome divergence in the course of evolution. It is suggested that they are close to the initial primitive sequences existing on ancient supercontinents, whereas continent-specific BSs were formed after continent separation. Comparison of all currently known BSs in the sequence pool of the genus Chironomus showed that the genomes of the most distant species differed by more than 90 inversion breaks, causing changes of their linear structure. In such cases, conserved genome regions span about 10 bands.
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