Non-repetitive DNA sequence divergence in phylogenetically diploid and tetraploid teleostean species of the family cyprinidae and the order isospondyli
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Non-repetitive DNA of anciently tetraploid teleostean species was analysed for the presence of duplicated sequences. Closely related diploid species were investigated in comparison. From the reassociation kinetics of total nuclear DNA, rate constants and fraction sizes of classes of repetitive and non-repetitive sequences were determined. DNA fractions enriched in the slowest renaturing sequence class were prepared and subjected to reassociation. The rate constants of these reactions were compared with the values expected for single-copy DNA from analytical genome size determinations. From reassociated DNA enriched in non-repetitive sequences also the melting temperatures were determined as a measure of internal base sequence heterogeneity. It has been shown that the two ancient tetraploids Cyprinus carpio and Thymallus thymallus are, with regard to the thermal stability of reassociated non-repetitive DNA, and with regard to the correspondence of reaction rates with the values expected for single copy DNA, indistinguishable from diploid controls (Rutilus rutilus, Clupea harengus and Sprattus sprattus). The tetraploid species Salmo irideus, Salvelinus fontinalis and Coregonus lavaretus appear as very recent tetraploids with regard to these criteria. The significance of the results for estimating the time of occurence of polyploidisation events in these taxa is discussed.
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