Comparative chromosome mapping of repetitive sequences. Implications for genomic evolution in the fish, Hoplias malabaricus

Marcelo B Cioffi,Cesar Martins,Luiz Ac Bertollo

doi:10.1186/1471-2156-10-34

Abstract

BackgroundSeven karyomorphs of the fish, Hoplias malabaricus (A-G) were previously included in two major groups, Group I (A, B, C, D) and Group II (E, F, G), based on their similar karyotype structure. In this paper, karyomorphs from Group I were analyzed by means of distinct chromosomal markers, including silver-stained nucleolar organizer regions (Ag-NORs) and chromosomal location of repetitive sequences (18S and 5S rDNA, and satellite 5SHindIII-DNA), through fluorescence in situ hybridization (FISH), in order to evaluate the evolutionary relationships among them.ResultsThe results showed that several chromosomal markers had conserved location in the four karyomorphs. In addition, some other markers were only conserved in corresponding chromosomes of karyomorphs A-B and C-D. These data therefore reinforced and confirmed the proposed grouping of karyomorphs A-D in Group I and highlight a closer relationship between karyomorphs A-B and C-D. Moreover, the mapping pattern of some markers on some autosomes and on the chromosomes of the XY and X1X2Y systems provided new evidence concerning the possible origin of the sex chromosomes.ConclusionThe in situ investigation of repetitive DNA sequences adds new informative characters useful in comparative genomics at chromosomal level and provides insights into the evolutionary relationships among Hoplias malabaricus karyomorphs.

Highlights

Seven karyomorphs of the fish, Hoplias malabaricus (A-G) were previously included in two major groups, Group I (A, B, C, D) and Group II (E, F, G), based on their similar karyotype structure
Despite differences in diploid chromosome number and in the presence or absence of differentiated sex chromosome systems, the seven karyomorphs were subdivided into two major groups (I and II) based on general karyotype similarity [1]
Sites of 5SHindIII-DNA, 5S rDNA and 18S rDNA were clearly detected by the fluorescence in situ hybridization (FISH) procedures, allowing their clear identification and location in the chromosomes of H. malabaricus (Figures 1, 2, 3 and 4)

Summary

Introduction

Seven karyomorphs of the fish, Hoplias malabaricus (A-G) were previously included in two major groups, Group I (A, B, C, D) and Group II (E, F, G), based on their similar karyotype structure. Usually reported as a single taxonomic entity, Hoplias malabaricus (Characiformes, Erythrinidae) has significant karyotypic diversity and well-defined population differences concerning the diploid number, morphology of chromosomes and sex chromosome systems. Such intraspecific diversity enabled the characterization of seven main karyomorphs (A-G), in which those without differentiated sex chromosome systems (A, C, E and F). Despite differences in diploid chromosome number and in the presence or absence of differentiated sex chromosome systems, the seven karyomorphs were subdivided into two major groups (I and II) based on general karyotype similarity [1]. Group I included karyomorphs A-D, while Group II included karyomorphs E-G (Table 1).

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Results

Discussion

Conclusion