Several lines of evidence suggest that reiterated sequences in the human genome are targets for nonallelic homologous recombination (NAHR), which facilitates genomic rearrangements. We have used a PCR-based approach to identify breakpoint regions of rearranged structures in the human genome. In particular, we have identified intrachromosomal identical repeats that are located in reverse orientation, which may lead to chromosomal inversions. A bioinformatic workflow pathway to select appropriate regions for analysis was developed. Three such regions overlapping with known human genes, located on chromosomes 3, 15, and 19, were analyzed. The relative proportion of wild-type to rearranged structures was determined in DNA samples from blood obtained from different, unrelated individuals. The results obtained indicate that recurrent genomic rearrangements occur at relatively high frequency in somatic cells. Interestingly, the rearrangements studied were significantly more abundant in adults than in newborn individuals, suggesting that such DNA rearrangements might start to appear during embryogenesis or fetal life and continue to accumulate after birth. The relevance of our results in regard to human genomic variation is discussed.

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Most species of the genus Harttia inhabits the headwaters of small tributaries, but some species are restricted to the main channel of some rivers. This feature, combined with limited dispersal ability, leads to the formation of small isolated populations with reduced gene flow. Currently, there are 23 taxonomically defined and recognized species, and 17 of these are found in Brazil, distributed in several hydrographic basins. Despite this diversity, few chromosomal data for the species belonging to this genus are found in the literature. Thus, this study analyzed, by classical and molecular cytogenetics methodologies, the chromosomal diversity of this genus, to discuss the processes that are involved in the evolution and karyotype differentiation of the species of the group. Seven species of Harttia were analyzed: H. kronei, H. longipinna, H. gracilis, H. punctata, H. loricariformis, H. torrenticola, and H. carvalhoi. The chromosomal diversity found in these species includes different diploid and fundamental numbers, distinct distribution of several repetitive sequences, the presence of supernumerary chromosomes in H. longipinna and multiple sex chromosome systems of the type XX/XYY in H. carvalhoi and XXXX/XXY in H. punctata. Lastly, our data highlight the genus Harttia as an excellent model for evolutionary studies.

Harttia is a genus in the subfamily Loricariinae that accommodates fishes popularly known as armored catfishes. They show extensive karyotypic diversity regarding interspecific numerical/structural variation of the karyotypes, with the presence of the XX/XY1Y2 multiple sex chromosome system, as found in H. carvalhoi. In this context, this study aimed to characterize Harttia punctata chromosomally, for the first time, and to infer the rearrangements that originated the X1X1X2X2/X1X2Y multiple sex chromosome system present in this species. The data obtained in this study, with classical (Giemsa, C-banding and AgNORs) and molecular methodologies (fluorescence in situ hybridization) and chromosome microdissection, indicated that a translocation between distinct acrocentric chromosomes bearing rRNA genes, accompanied by deletions in both chromosomes, might have originated the neo-Y chromosome in this species. The data also suggest that the multiple sex chromosome systems present in H. carvalhoi and H. punctata had an independent origin, evidencing the recurrence of chromosome alterations in species from this genus.

Karyotypic analyses were performed in fishes from the genus Hoplias (H. malabaricus and H. lacerdae groups) from the São Francisco River basin (Brazil), in an impacted region by a river transposition which altered the local ecology and fish fauna. The karyotypes were investigated using chromosomal markers obtained from classic and molecular cytogenetics (Giemsa, CMA 3 and DAPI staining, C-banding, Ag-NORs, and FISH with 18S rDNA, 5S rDNA and 5SHindIII satellite DNA probes). Two karyotypic forms were found for the H. malabaricus group-karyomorph F, corresponding to the native form from the São Francisco River basin, and karyomorph A, corresponding to the invading form from the Upper Paraná River basin. Specimens from the H. lacerdae group exhibited striking chromosome differences in relation to the H. malabaricus group, thereby enabling good cytotaxonomic characterization and inferences regarding the karyotype evolution of these groups.

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ABSTRACT. We examined chromosomes of three species of the genus Hypostomus, in order to contribute to the understanding of the karyotype evolution of this group. Specimens of H. ancistroides and H. nigromaculatus displayed differences in karyotype formulas, distribution and location of heterochromatin and nucleolus organizer regions when compared to other populations of the same species. We made the first cytogenetic characterization of H. tapijara, an endemic species in the Ribeira de Iguape River. These specimens had 2n = 66 chromosomes, while H. ancistroides showed 2n = 68 and H. nigromaculatus 2n = 76 chromosomes. Physical mapping of 18S and 5S rDNA sites of the three species showed simple, multiple and syntenic clusters. Synteny of ribosomal sites was found in H. ancistroides and H. tapijara, and an interspersed pattern between these sites in all chromosomes bearing the synteny was observed. We conclude that the genus Hypostomus has a high chromosome complexity that is accompanied by great morphological variation. It is evident that this group comprises an interesting model for understanding the chromosome evolution of Neotropical ichthyofauna.

Hypostominae is the largest subfamily of Loricariidae, and is widely distributed throughout the Neotropic. In the present article, we analyze three Loricariidae species that were considered part of Hypostominae, from three different tribes, to discuss chromosome evolution in this fish group and to review the existent data for the subfamily. Rhinelepis aspera had 54 chromosomes (20m + 26sm+8st), whereas Pterygoplichthys ambrosettii and Megalancistrus parananus had 52 chromosomes, with 16m+24sm+8st+4a and 18m+24sm+10st, respectively. The karyological data were compared with existent phylogenetic hypotheses, indicating a common ancestor with 2n = 52 chromosomes for the Acanthicus, Hemiancistrus, and Peckoltia clades, as well as for Hypostomini. Shared recurrent characteristics of the tribes are discussed, as well as peculiarities of genera Ancistrus and Hypostomus. We propose that the occurrence of fragile sites demonstrated for Ancistrus facilitated chromosomal rearrangements that decreased the proportion of metacentric/submetacentric chromosomes and the diploid number in many species from this genus. Although Hypostominae is usually considered a subfamily with derived chromosome features, our revision shows that this is valid only for Hypostomini and Ancistrini, which have a divergent chromosome evolution from other tribes that seems to conserve plesiomorphic features.