Mitochondrial DNA (mtDNA) restriction analysis was used to examine the evolutionary and taxonomic relationships among 11 taxa of the subfamily Salmoninae. The genera Brachymystax and Hucho were closely related, diverging by sequence divergence estimates of 3·1%. Because the mtDNA sequence divergence between blunt-and sharp-snouted forms of Brachymystax (2·24%) was similar to divergence level of Brachymystax and Hucho, then taking into account the distinct morphological, ecological and allozyme differences between them, it is possible to recognize these forms as two separate species. The subgenus Parahucho formed a very distinct group differing by 6·35-7·08% (sequence divergence estimate) from both Brachymystax and Hucho and must be considered as a valid genus. The UPGMA and neighbour-joined phenograms showed that the five genera studied are divided into two main groupings: (1) Hucho, Brachymystax and Salvelinus; and (2) Oncorhynchus and Parahucho species. The mtDNA sequence divergence estimates between these groupings were about 8·1%. However, the subsequent bootstrap analysis of mtDNA RFLP data did not support the monophyly of the latter grouping. The concordance of morphological and mtDNA phylogenetic patterns is discussed. 1996 The Fisheries Society of the British Isles
Kinetic of reassociation of short DNA fragments were measured in eight ground squirrel species: Citellus undulatus, C. parryL C. relictus, C. dauricus, C. citellus, C. pygmaeus, C. fulvus and C. major. It was shown that 30-50% of their genome were represented by repeated sequences forming three kinetic fractions, i,e., very fast(Cot< 10 3), fast(Cot 10 -3 -3 × I0 -l) and intermediate (Cot 6 × 10 -1 -6 × 101). Based on parameters of DNA reassociation kinetics genome sizes of Citellus were estimated to range from 2.7 pg (C. dauricus) to 3.9 pg (C. pygmaeus and C.fulvus). Variation in genome sizes involves both the repeated and the non-repeated sequence components to approximately equal extents in all the species except C. dauricus. The linear quantitative relation between C-banding heterochromatin and both very fast and fast reassociated DNA fractions was established, but no connection with the intermediate fraction was found. No distinct relation was revealed between parameters of DNA reassociation kinetics and taxonomic status of species within genus or with the chromosome number of the karyotype.
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