FIELD: genetic engineering, medicinal genetics. SUBSTANCE: invention relates to constructing the new molecular-genetic marker of 13-th and 21-d human chromosomes that shows specificity with respect to centimeter region involving heterochromatin of both arms. This nucleotide sequence relates to class of alphoid DNA (on the basis of data of DNA-probe restriction mapping, blot-hybridization and chromosome hybridization in situ). New recombinant plasmid has human DNA genome fragment (size is 680 base pairs) that contains two internal unique restriction site PstI and genome fragment flanking with Eco RI-site from the different ends. Also, this new DNA-probe shows minor hybridization site on human chromosomes in situ that involves chromosomes 2, 4, 14, 15, 18, 20 and 22. This DNA- probe hybridizes only with centimeter regions of human chromosome 13 and 21. Plasmid can be used for diagnosis of chromosomal pathology (Down's and Pataw's syndromes). EFFECT: improved method of chromosome marking.
