Genome size and chromatin condensation in vertebrates.

Cell membrane-dependent chromatin condensation was studied by flow cytometry in erythrocytes of 36 species from six classes of vertebrates. A positive relationship was found between the degree of condensation and genome size. The distribution of variances among taxonomic levels is similar for both parameters. However, chromatin condensation varied relatively more at the lower taxonomic levels, which suggests that the degree of DNA packaging might serve for fine-tuning the 'skeletal' and/or 'buffering' function of noncoding DNA (although the range of this fine-tuning is smaller than the range of genome size changes). For two closely related amphibian species differing in genome size, change in chromatin condensation under the action of elevated extracellular salinity was investigated. Condensation was steadier and its reaction to changes in solvent composition was more inertial in the species with a larger genome, which is in agreement with the buffering function postulated for redundant DNA. The uppermost genome size in vertebrates (and in living beings in general) was updated using flow cytometry and was found to be about 80 pg (78,400 Mb). The widespread opinion that the largest genome occurs in unicellular organisms is rejected as being based on artifacts.