Abstract
The chromosomal characteristics, locations and variations of the C-band positive heterochromatin and telomeric DNA sequences were studied in the European grayling karyotype (Thymallus thymallus, Salmonidae) using conventional C-banding, endonucleases digestion banding, silver nitrate (AgNO3), chromomycin A3 and 4′,6-diamidino-2-phenylindole staining techniques as well as fluorescence in situ hybridization (FISH) and primed in situ labelling. Original data on the chromosomal distribution of segments resistant to AluI restriction endonuclease and identification of the C-banded heterochromatin presented here have been used to characterize the grayling karyotype polymorphism. Structural and length polymorphism of the chromosome 21 showing a conspicuous heterochromatin block adjacent to the centromere seems to be the result of the deletion and inversion. Two pairs of nuclear organizer regions (NOR)-bearing chromosomes were found to be polymorphic in size and displaying several distinct forms. FISH with telomeric peptide nucleic acid probe enabled recognition of the conservative telomeric DNA sequences. The karyotype of the thymallid fish is thought to experienced numerous pericentric inversions and internal telomeric sites (ITSs) observed at the pericentromeric regions of the six European grayling metacentric chromosomes are likely relics of the these rearrangements. None of the ITS sites matched either chromosome 21 or NOR bearing chromosomes.
Highlights
The common ancestor of the Salmonidae family experienced a whole genome duplication (WGD) event between 25 and 100 million years ago (Allendorf and Thorgaard 1984)
Structural and length polymorphism of the chromosome 21 showing a conspicuous heterochromatin block adjacent to the centromere seems to be the result of the deletion and inversion
C-banding and restriction enzyme digestion applied for the first time in the European grayling chromosomes enabled characteristics of the heterochromatin variation in this species
Summary
The common ancestor of the Salmonidae family experienced a whole genome duplication (WGD) event between 25 and 100 million years ago (Allendorf and Thorgaard 1984). The hypothetical karyotype of the first tetraploid ancestor has been proposed to comprise 96 uni-armed chromosomes (Phillips and Rab 2001). Genomes of the extant salmonid fishes have undergone rediploidization process including numerous chromosomal rearrangements and leading to formation of many different karyotypes with chromosome number ranging from 52 to 102 (NF = 72–168) (Phillips and Rab 2001). In the contrary to the species from Salmoninae and Coregoninae subfamilies, graylings (Thymallinae) are rather poorly cytogenetically studied salmonids and only three species have been examined to date: Thymallus thymallus (Nygren et al 1971; Kalat et al 1988; Jankun et al 2003), T. arcticus (Makoedov 1982; Severin 1986) and T. grubii (Makoedov 1987). Characteristics of the grayling karyotype differ from what is observed in the other salmonids. While most of the salmonids show chromosome
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