Satellite DNA (satDNA) is an abundant fraction of repetitive DNA in eukaryotic genomes and plays an important role in genome organization and evolution. In general, satDNA sequences follow a concerted evolutionary pattern through the intragenomic homogenization of different repeat units. In addition, the satDNA library hypothesis predicts that related species share a series of satDNA variants descended from a common ancestor species, with differential amplification of different satDNA variants. The finding of a same satDNA family in species belonging to different genera within Characidae fish provided the opportunity to test both concerted evolution and library hypotheses. For this purpose, we analyzed here sequence variation and abundance of this satDNA family in ten species, by a combination of next generation sequencing (NGS), PCR and Sanger sequencing, and fluorescence in situ hybridization (FISH). We found extensive between-species variation for the number and size of pericentromeric FISH signals. At genomic level, the analysis of 1000s of DNA sequences obtained by Illumina sequencing and PCR amplification allowed defining 150 haplotypes which were linked in a common minimum spanning tree, where different patterns of concerted evolution were apparent. This also provided a glimpse into the satDNA library of this group of species. In consistency with the library hypothesis, different variants for this satDNA showed high differences in abundance between species, from highly abundant to simply relictual variants.

Most Meliponini share a distinctive pattern of heterochromatin distribution in relation to other bees. In general, they present one euchromatic and one heterochromatic chromosome arm, a feature explained by minimum interaction theory, which involved centric fissions followed by heterochromatin addition. In this work, two Meliponini with a distinct pattern of heterochromatin distribution, Tetragonisca fiebrigi and Melipona rufiventris, were analyzed using chromosomal microdissection of the heterochromatin region followed by FISH (fluorescent in situ hybridization). Hybridization revealed FISH signals equivalent to location of the isolated fragment that were widespread over heterochromatic portions of other chromosomes. This result showed that the heterochromatic sequences were very similar among chromosomes in the same species. Cross-hybridization of each probe in M. rufiventris and T. fiebrigi yielded no signals, revealing that both species presented differentiated and non-homologous heterochromatin sequences.

B chromosomes are dispensable genomic elements found in different groups of animals and plants. In the present study, a whole chromosome probe was generated from a specific heterochromatic B chromosome occurring in cells of the characidae fish Moenkhausia sanctaefilomenae (Steindachner, 1907). The chromosome painting probes were used in fluorescence in situ hybridization (FISH) experiments for the assessment of metaphase chromosomes obtained from individuals from three populations of Moenkhausia sanctaefilomenae. The results revealed that DNA sequences were shared between a specific B chromosome and many chromosomes of the A complement in all populations analyzed, suggesting a possible intra-specific origin of these B chromosomes. However, no hybridization signals were observed in other B chromosomes found in the same individuals, implying a possible independent origin of B chromosome variants in this species. FISH experiments using 18S rDNA probes revealed the presence of non-active ribosomal genes in some B chromosomes and in some chromosomes of the A complement, suggesting that at least two types of B chromosomes had an independent origin. The role of heterochromatic segments and ribosomal sequences in the origin of B chromosomes were discussed.

-The emergence of new molecular biology techniques has provided cytogenetics with tools which allow for the elucidation of questions that classical cytogenetics could not answer. Therefore, the present work standardizes a microdissection protocol for cytogenetic studies in bees. This methodology was first used in these insects and may contribute greatly to studies involving chromosomal rearrangements, heterochromatin composition, B chromosomes and others. For this study, the centromeric region of chromosomes in the stingless bee Tetragonisca fiebrigi was used for probe synthesis. The results demonstrated that the methodology used was efficient, presenting markings in the centromeric regions of several chromosomes. Hybridization in other sites indicates that the probe was able to detect regions that present homology with its sequence. This indicates that the technique is effective to study chromosomal evolution, genome organization and even the origin of B chromosomes.

Several cytogenetic studies in Prochilodus lineatus (Valenciennes 1836) describe a striking system of supernumerary microchromosomes revealing the occurrence of three morphological types visualized as acrocentric, metacentric and submetacentric. The present study aimed to compare the DNA homology among the B chromosome variants, as well as the components of the standard complement using total B specific probes obtained by microdissection. This technique, which allows direct isolation of DNA from each B chromosome variant of interest, was applied to obtain the probes. Accordingly, cross hybridizations targeting all types were performed by using the fluorescence in situ hybridization technique. The results obtained revealed signals of hybridization on all kinds of B chromosomes, indicating homology among the variants. Moreover, markings on the standard A complement were observed using the B submetacentric chromosome specific probe. Based on these data, we can infer that B chromosome variants in P. lineatus have homologous regions, suggesting a common origin from an ancestral variant. Furthermore, it can be also hypothesized that the primitive supernumerary was probably originated from elements of the standard complement, since the B submetacentric morphotype shares sequences with the centromeric region of some chromosomes of the A complement.

Direitos para esta edição cedidos à Atena Editora pelos autores. Open access publication by Atena Editora Todo o conteúdo deste livro está licenciado sob uma Licença de Atribuição Creative Commons. Atribuição-Não-Comercial-NãoDerivativos 4.0 Internacional (CC BY-NC-ND 4.0). O conteúdo dos artigos e seus dados em sua forma, correção e confiabilidade são de responsabilidade exclusiva dos autores, inclusive não representam necessariamente a posição oficial da Atena Editora. Permitido o download da obra e o compartilhamento desde que sejam atribuídos créditos aos autores, mas sem a possibilidade de alterá-la de nenhuma forma ou utilizá-la para fins comerciais.Todos os manuscritos foram previamente submetidos à avaliação cega pelos pares, membros do Conselho Editorial desta Editora, tendo sido aprovados para a publicação com base em critérios de neutralidade e imparcialidade acadêmica.A Atena Editora é comprometida em garantir a integridade editorial em todas as etapas do processo de publicação, evitando plágio, dados ou resultados fraudulentos e impedindo que interesses financeiros comprometam os padrões éticos da publicação. Situações suspeitas de má conduta científica serão investigadas sob o mais alto padrão de rigor acadêmico e ético.

Direitos para esta edição cedidos à Atena Editora pelos autores. Open access publication by Atena Editora Todo o conteúdo deste livro está licenciado sob uma Licença de Atribuição Creative Commons. Atribuição-Não-Comercial-NãoDerivativos 4.0 Internacional (CC BY-NC-ND 4.0). O conteúdo dos artigos e seus dados em sua forma, correção e confiabilidade são de responsabilidade exclusiva dos autores, inclusive não representam necessariamente a posição oficial da Atena Editora. Permitido o download da obra e o compartilhamento desde que sejam atribuídos créditos aos autores, mas sem a possibilidade de alterá-la de nenhuma forma ou utilizá-la para fins comerciais.Todos os manuscritos foram previamente submetidos à avaliação cega pelos pares, membros do Conselho Editorial desta Editora, tendo sido aprovados para a publicação com base em critérios de neutralidade e imparcialidade acadêmica.A Atena Editora é comprometida em garantir a integridade editorial em todas as etapas do processo de publicação, evitando plágio, dados ou resultados fraudulentos e impedindo que interesses financeiros comprometam os padrões éticos da publicação. Situações suspeitas de má conduta científica serão investigadas sob o mais alto padrão de rigor acadêmico e ético.

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