[A comparative study of Dicrostonyx torquatus chionopaes Allen DNA with different numbers of B-chromosomes].

In order to elucidate the possible relationship between the karyotype and the polynucleotide sequence organization in DNA, comparison was made between DNA from the liver of Dicrostonyx torquatus chionapaes Allen with different numbers of B-chromosomes (2n = 47-49, 1-3 B-chromosomes; 2n = 52-54,6-8 B-chromosomes). The reassociation kinetics patterns for denatured DNA fragments (about 300 nucleotides long) were obtained by the batch hydroxyapatite method. The analysis of these patterns showed a approximately 10% increase in the proportion of reiterated nucleotide sequences in the DNA of animals with 6-8 B-chromosomes. The increase in the proportion of reiterations in DNA correlated with increase in the number of B-chromosomes can be regarded as an indirect confirmation of the heterochromatic nature of B-chromosomes. The individual fractions of reiterated nucleotide sequences (C0t = 1.0) were isolated from studied DNas. The reassociation kinetics of these fractions and the thermostability of resulting duplexes were examined. The revealed differences are indicative of a certain dissimilarity in the polynucleotide sequences organization that correlate with variation in the number of B-chromosomes. The heterochromatic and euchromatic. DNAas from the liver cell nuclei of animals carrying different numbers of B-chromosomes were studied by thermal denaturation analysis and neutral CsCl equilibrium centrifugation. In the heterochromatic DNAs from livers of D. t. chionopaes with 6-8 B-chromosomes additional components enriched with AT-pairs were revealed. The specific features of DNA correlated with increase in the number of B-chromosomes are discussed in connection with peculiarities of B-chromosomes behaviour and their evolution in Dicrostonyx torquatus chionapaes.