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Karyotype diversity and patterns of chromosomal evolution in Eigenmannia (Teleostei, Gymnotiformes, Sternopygidae).

ABSTRACT: Conventional (Giemsa, C-banding, Ag - NORs) and molecular [5S rDNA, 18S rDNA, (TTAGGG)n] cytogenetic techniques were employed to study six species of the genus Eigenmannia Jordan & Evermann, 1896. They exhibited diploid chromosome numbers ranging from 2n=28 (Eigenmannia sp.1) to 2n=38 (Eigenmanniavirescens (Valenciennes, 1836)). The C-banding results revealed that species with the lowest 2n have less heterochromatin content and that morphologically differentiated sex chromosomes observed in two species showed distinct patterns of heterochromatin. While the X1, X2 and Y-chromosomes of Eigenmannia sp.2 showed only centromeric heterochromatin, the XY sex chromosomes of Eigenmanniavirescens possessed large heterochromatic blocks in the terminal position, particularly on the X chromosome. The nucleolus organizer regions (NORs) were located in different positions when compared to the 5S rDNA sites. Additionally, the presence of minor ribosomal gene sites on the sex chromosome pair of Eigenmanniavirescens represented a new type of the sex chromosomes in this group. The telomeric probe (TTAGGG)n hybridized to the terminal portion of all chromosomes in all species examined however, interstitial telomeric sites were found in the metacentric pair No. 2 in Eigenmannia sp.1. The analyzes confirmed some hypotheses about karyotype evolution in the genus Eigenmannia, and brought new information about the distribution of the genetic material in the chromosomes of the samples analyzed providing new insights for understanding the process differentiation in the genomes of species under study.

SUBMITTER: Sene VF

PROVIDER: S-EPMC4296717 | biostudies-other | 2014

REPOSITORIES: biostudies-other

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Project description:BackgroundThe Trypanosoma cruzi genome was sequenced from a hybrid strain (CL Brener). However, high allelic variation and the repetitive nature of the genome have prevented the complete linear sequence of chromosomes being determined. Determining the full complement of chromosomes and establishing syntenic groups will be important in defining the structure of T. cruzi chromosomes. A large amount of information is now available for T. cruzi and Trypanosoma brucei, providing the opportunity to compare and describe the overall patterns of chromosomal evolution in these parasites.Methodology/principal findingsThe genome sizes, repetitive DNA contents, and the numbers and sizes of chromosomes of nine strains of T. cruzi from four lineages (TcI, TcII, TcV and TcVI) were determined. The genome of the TcI group was statistically smaller than other lineages, with the exception of the TcI isolate Tc1161 (José-IMT). Satellite DNA content was correlated with genome size for all isolates, but this was not accompanied by simultaneous amplification of retrotransposons. Regardless of chromosomal polymorphism, large syntenic groups are conserved among T. cruzi lineages. Duplicated chromosome-sized regions were identified and could be retained as paralogous loci, increasing the dosage of several genes. By comparing T. cruzi and T. brucei chromosomes, homologous chromosomal regions in T. brucei were identified. Chromosomes Tb9 and Tb11 of T. brucei share regions of syntenic homology with three and six T. cruzi chromosomal bands, respectively.ConclusionsDespite genome size variation and karyotype polymorphism, T. cruzi lineages exhibit conservation of chromosome structure. Several syntenic groups are conserved among all isolates analyzed in this study. The syntenic regions are larger than expected if rearrangements occur randomly, suggesting that they are conserved owing to positive selection. Mapping of the syntenic regions on T. cruzi chromosomal bands provides evidence for the occurrence of fusion and split events involving T. brucei and T. cruzi chromosomes.

Project description:BACKGROUND:Prospero (Hyacinthaceae) provides a unique system to assess the impact of genome rearrangements on plant diversification and evolution. The genus exhibits remarkable chromosomal variation but very little morphological differentiation. Basic numbers of x?=?4, 5, 6 and 7, extensive polyploidy, and numerous polymorphic chromosome variants were described, but only three species are commonly recognized: P. obtusifolium, P. hanburyi, and P. autumnale s.l., the latter comprising four diploid cytotypes. The relationship between evolutionary patterns and chromosomal variation in diploids, the basic modules of the extensive cytological diversity, is presented. RESULTS:Evolutionary inferences were derived from fluorescence in situ hybridization (FISH) with 5S and 35S rDNA, genome size estimations, and phylogenetic analyses of internal transcribed spacer (ITS) of 35S rDNA of 49 diploids in the three species and all cytotypes of P. autumnale s.l. All species and cytotypes possess a single 35S rDNA locus, interstitial except in P. hanburyi where it is sub-terminal, and one or two 5S rDNA loci (occasionally a third in P. obtusifolium) at fixed locations. The localization of the two rDNA types is unique for each species and cytotype. Phylogenetic data in the P. autumnale complex enable tracing of the evolution of rDNA loci, genome size, and direction of chromosomal fusions: mixed descending dysploidy of x?=?7 to x?=?6 and independently to x?=?5, rather than successive descending dysploidy, is proposed. CONCLUSIONS:All diploid cytotypes are recovered as well-defined evolutionary lineages. The cytogenetic and phylogenetic approaches have provided excellent phylogenetic markers to infer the direction of chromosomal change in Prospero. Evolution in Prospero, especially in the P. autumnale complex, has been driven by differentiation of an ancestral karyotype largely unaccompanied by morphological change. These new results provide a framework for detailed analyses of various types of chromosomal rearrangements and karyotypic variation in polyploids.

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Karyotype diversity and patterns of chromosomal evolution in Eigenmannia (Teleostei, Gymnotiformes, Sternopygidae).

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