[The length of chromatin loops in meiotic prophase I of warm-blooded vertebrates depends on the DNA compositional organization].

In meiotic prophase I, chromatin fibrils attached to the lateral elements of the synaptonemal complexes (SC) form loops. SCAR DNA (synaptonemal complex associated regions of DNA) is a family of genomic DNA tightly associated with the SC and located at the chromatin loop basements. Using the hybridization technique, it was demonstrated that localization of SCAR DNA was evolutionarily conserved in the isochore compositional fractions of the three examined genomes of warm-blooded vertebrates—human, chicken, and golden hamster. The introduction of the concept of the comparative loops (CL) of DNA that form of chromatin attach to SC in the isochore compositional fractions provided the calculation of their length. An inverse proportional relationship between the length of CL DNA and the GC level in the isochore compartments of the studied warm-blooded vertebrate genomes was revealed. An exception was the GCpoorest L1 isochore family. For different compositional isochores of the human and chicken genomes, the number of genes in the CL DNA was evaluated. A model of the formation of GC-rich isochores in vertebrate genomes, according to which there was not only an increase in the GC level but also the elimination of functionally insignificant noncoding DNA regions, as well as joining of isochores decreasing in size, was suggested.