B Chromosome Variability in Plants and Animals under Extreme Environments

Data on B chromosomes in populations of different systematic groups of plants and animals from extreme habitats, i.e., the range boundaries and its parts exposed to adverse environmental factors are reviewed. Analysis showed rather similar patterns of B chromosome distribution in the species extreme habitats. In particular, a tendency to the increased polymorphism and increase in B chromosome number and frequency, which was accompanied by changes in the karyotype, as well as genomic and chromosomal abnormalities in their carriers, was observed. B chromosomes are often found in species with wide ranges. The possible adaptive role of B chromosomes in the vital activity of organisms and the genome evolution is discussed.