[Chromatin diminution at the border of the XX and XXI centuries].

The size of genomes in eukaryotic organisms is one of the greatest mysteries of biology. As known from the middle of the XX century, the level of organization of a particular organism, does not depend on its genome size, i. e. on DNA amount in the nucleus. We believe that an actual function of non-coding DNA stands behind the phenomenon of chromatin diminution, known already for 100 years. Diminution of chromatin normally takes place in cells involved in body building and never occurs in developmental precursors of germ cells. Apparently, the former are cells, in which non-coding DNA is functionally significant. We cloned a fraction of DNA eliminated during chromatin diminution of Cyclops kolensis (Cyclopoida, Crustascea) and sequenced 90 clones totally making 32 kb. Taken together, the provided evidence has demonstrated a high organization ordering of DNA sequences restricted to the germ line. Chromatin diminution never takes place in human cells and in cells of the majority of animals. These cells may isolate non-coding DNA in other ways, making it unreactable for most enzymes and thus functionally cut off. Thus, a certain part of genome with a particular size and structure may serve for genetic isolation of species as shellfish or junk DNA are vital components rather than pieces of garbage.