The specific blocks of heterochromatin on metaphase chromosomes of horse and Prjewalski horse detected by in situ digestion with restriction endonucleases

Restriction endonuclease in situ digestion of metaphase chromosomes gives an opportunity to reveal strips with different structure within GC-rich pericentric heterochromatin of the domestic horse and the wild Przewalski horse. Blocks of heterochromatin, which are insensitive to HaeIII and brightly stained with chromomycin A3 after restriction enzyme digestion, are localized on the border with euchromatin in the majority of chromosomes of Equus caballus and E. przewalskii. In contrast to chromosome 5 of E. caballus, acrocentric chromosomes of E. prezewalskii which are homologous to this chromosome have RE-CMA-blocks. We discuss a possible nature of the specific heterochromatin, which is insensitive to restriction enzyme digestion, and its role in the karyotype evolution.