USE OF CLONED ALPHA-SATELLITE DNA PROBES FOR THE ANALYSIS OF POLYMORPHIC HETEROCHROMATIC REGIONS OF HUMAN ACROCENTRIC CHROMOSOMES AND PARENTAL ORIGIN OF TRISOMY-21

Chromosomal distribution of cloned human alpha-satellite DNA alphaR1-6 has been studied by in situ hybridization technique. The sequence under study has been shown to be predominantly located in the centromeric regions of chromosomes 13 and 21. Intercellular variability of labelling patterns in every person under analysis being insignificant, there exists strong individual variability of interchromosomal distribution of the satellite. This variability leads to the differences of the chromosome labelling density (i.e. the number of satellite DNA copies) both between and within chromosome pairs. The difference in the copy number between two homologoues chromosomes, 13 and 21 reaches up to 5 times. No correlation between nondisjunction and the number of copies of alpha-satellite DNA was found. Analysis of individual distribution of satellite between homologoues of chromosome 21 provides new possibilities for determination of the origin of extra chromosome in the patients with trisomy 21.