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Ameerega trivittata is a widely distributed dendrobatid species with colour polymorphism for which only the diploid number, nucleolar organizer regions (NORs) and heterochromatic pattern are known. Here, we investigated the existence of cytogenetic structure in A. trivittata populations with different morphotypes. Four morphotypes and their geographical distributions were defined. All the individuals have 24 chromosomes and a similar heterochromatic pattern, the same location of telomeric regions and 5S rDNA. The NOR site was coincident with the 18S rDNA in pair 9, but some individuals presented an additional site in one of the homologues of pair 11. The highest variation was found in the microsatellite distribution patterns. Comparing the cytogenetic characters of the individuals, two groups were detected: (1) Tabatinga (morphotype B) and Benjamin Constant (morphotype A), and (2) Presidente Figueiredo and Tefé (morphotype C). The cytogenetic data appear to be correlated to the structure pattern of the morphotypes, and corroborate the dispersal routes proposed in the literature. This is the first study of population cytogenetics for the group. Our results provide a series of cytogenetic characters for A. trivittata and for Dendrobatidae for the first time and highlight the importance of considering cytogenetics in population research.

MeliponaIlliger, 1806 is represented by 74 known species of stingless bees, distributed throughout the Neotropical region. Cytogenetically it is the most studied stingless bee genus of the tribe Meliponini. Member species are divided in two groups based on the volume of heterochromatin. This study aim was to analyze the composition and organization of chromatin of the stingless bee subspeciesMelipona seminigra merrillaeCockerell, 1919 using classical and molecular cytogenetic techniques, so contributing to a better understanding of the processes of chromosomal changes within the genus. We confirm thatM. seminigra merrillaehas a chromosome number of 2n = 22 and n = 11, results that differ from those reported for the genus in the absence of B chromosomes. The heterochromatic pattern revealed a karyotype composed of chromosomes with a high heterochromatin content, which makes it difficult to visualize the centromere. Silver nitrate impregnation (Ag-NOR) showed transcriptionally active sites on the second chromosomal pair. Staining of base-specific fluorophores DAPI-CMA3indicated a homogeneous distribution of intensely DAPI-stained heterochromatin, while CMA3markings appeared on those terminal portions of the chromosomes corresponding to euchromatin. Similar to Ag-NOR, fluorescence in situ hybridization (FISH) with 18S ribosomal DNA probe revealed distinct signals on the second pair of chromosomes. Microsatellite mapping (GA)15showed markings distributed in euchromatic regions, while mapping with (CA)15showed marking patterns in heterochromatic regions, together with a fully marked chromosome pair. Microsatellite hybridization, both in heterochromatic and euchromatic regions, may be related to the activity of transposable elements. These are capable of forming new microsatellites that can be dispersed and amplified in different regions of the genome, demonstrating that repetitive sequences can evolve rapidly, thus resulting in within-genus diversification.

The fish family Cynodontidae belongs to the superfamily Curimatoidea, together with the Hemiodontidae, Serrasalmidae, Parodontidae, Prochilodontidae, Chilodontidae, Curimatidae, and Anostomidae. The majority of the species of this superfamily that have been analyzed to date have a diploid chromosome number of 2n = 54. Differentiated sex chromosomes (with female heterogamety) have been observed only in the Prochilodontidae, Parodontidae, and Anostomidae. The present study provides the first description of differentiated sex chromosomes in the cynodontid species Cynodon gibbus, which has a ZZ/ZW system, and shows that repetitive DNA has played a fundamental role in the differentiation of these sex chromosomes.

Most of snakes exhibit a ZZ/ZW sex chromosome system, with different stages of degeneration. However, undifferentiated sex chromosomes and unique Y sex-linked markers, suggest that an XY system has also evolved in ancestral lineages. Comparative cytogenetic mappings revealed that several genes share ancestry among X, Y and Z chromosomes, implying that XY and ZW may have undergone transitions during serpent’s evolution. In this study, we performed a comparative cytogenetic analysis to identify homologies of sex chromosomes across ancestral (Henophidia) and more recent (Caenophidia) snakes. Our analysis suggests that, despite ~ 85 myr of independent evolution, henophidians and caenophidians retained conserved synteny over much of their genomes. However, our findings allowed us to discover that ancestral and recent lineages of snakes do not share the same sex chromosome and followed distinct pathways for sex chromosomes evolution.

The chromosomes of 2 flea beetle species from central Amazonia, Omophoita abbreviata and O. aequinoctialis (Alticini), were investigated through analysis of meiotic and mitotic cells. These species belong to the subtribe Oedionychina, a taxon that has unique cytogenetic features, such as giant sex chromosomes which are aligned at a distance during meiosis I (asynaptic). O. abbreviata and O. aequinoctialis have a meiotic formula of 10II + X + y, which is predominant in this subtribe. While the species of the genus Omophoita possess a relatively stable karyotype, a typical feature for Oedionychina, the present study identified inter- and intrapopulational variation in chromosome morphology, constitutive heterochromatin, and the presence and number of B chromosomes in O. aequinoctialis. In addition, FISH mapping of telomeric sequences revealed signals in the collochores, raising several questions on the chromosomal evolution in this group.

The organization and mapping of multigene families can produce useful genetic markers, and its use may elucidate the mechanisms of karyotype variation and genomic organization in different groups of eukaryotes. To date, few species of Coleoptera have been analyzed using FISH for the location of multigene families. The purpose of this study was to use high-resolution chromosome mapping to establish the genomic organization of the 18S rDNA, 5S rDNA and histone H3 gene families in Lagria villosa. FISH was performed using 18S rDNA, 5S rDNA and histone H3 probes prepared via PCR labeling. Fiber-FISH for 18S and 5S rDNA indicated that both ribosomal elements are colocalized in the short arm of chromosome 4. Additionally, FISH, using the histone H3 probe, revealed that this sequence is found in only one autosomal pair and did not colocalize with rDNA. Fiber-FISH with 5S and 18S probes, used to improve the mapping resolution of these regions, showed that both genes are closely interspersed with varying amounts of both DNA classes.

The HpaII/MspI-PCR is a method based on the sensitivity of restriction enzymes to methylation at their cleavage sites, which permits the comparison of the DNA methylation status of different organisms, based on the differential patterns of digestion. Prior to the present study, nothing was known of the methylation profile of specific DNA sequences in Amazonian fish based on enzymes sensitive to methylation. Given this, the present study investigated the methylation profile of the 18S rRNA gene of the armored catfish, Hoplosternum littorale, which inhabits relatively inhospitable environments in the Amazon basin. A differential methylation profile was found in the 18S rRNA sites, indicating that polluted environments may influence the methylation of DNA, and would have evolved in the species, initially, as a defense mechanism against the expression of transposable elements.

The order Coleoptera comprises species that are used as models in evolutionary studies, such as Alticinae, which features giant sex chromosomes. Thus, the aim of the present study was to investigate the differentiation and evolution of the sex chromosome in species of the Omophoita genus (Alticinae) using repetitive DNA (total C0t-1), C-banding and base-specific fluorochromes. Analyses using probes generated through C0t-1 reassociation kinetics showed markers distributed across all the chromosomes, especially the sex chromosomes. In conclusion, repetitive sequences are distributed across the sex chromosomes and autosomes, demonstrating that the heterochromatin of the species is largely composed of repetitive DNA. Cross-hybridisation among the species produced a very similar staining pattern for the probes. Thus, we conclude that the majority of the genome of the species of Omophoita is shared, showing the heterochromatin to be largely composed of repetitive DNA distributed along the sex chromosome...

The Xyp sex determination mechanism is the system most frequent and ancestral to Coleoptera. Moreover, the presence of argyrophilous material associated with the sex bivalent is described as being responsible for the maintenance and association of these chromosomes. There are no karyotype data available regarding the genus Lagria and no consensus in the literature regarding the argyrophilous material present in the lumen of sex bivalent. Therefore, the aim of this work was to investigate the mechanism of sex chromosome bivalent association in Lagria villosa by analyzing the argyrophilous nature of the material present in the Xyp lumen. It was also intended to characterize L. villosa cytogenetically. The analysis of meiotic cells showed 2n = 18 = 16+Xyp for males and 2n = 18 = 16+XX in females and the meiotic formula was 2n = 8II+Xyp. The C-banding showed blocks of pericentromeric heterochromatin in all chromosomes except in the yp chromosome. In these regions, the use of fluorochromes revealed the presence of heterochromatin containing GC rich DNA sequences. The study of synaptonemal complex showed a gradual increase in the electron-density of the axial elements of the sex chromosomes and their association with strongly electron-dense material. The pepsin pretreatment revealed that the material impregnated by silver is protein.

Repetitive DNA is the largest fraction of the eukaryote genome and comprises tandem and dispersed sequences. It presents variations in relation to its composition, number of copies, distribution, dynamics, and genome organization, and participates in the evolutionary diversification of different vertebrate species. Repetitive sequences are usually located in the heterochromatin of centromeric and telomeric regions of chromosomes, contributing to chromosomal structures. Therefore, the aim of this study was to physically map repetitive DNA sequences (5S rDNA, telomeric sequences, tropomyosin gene 1, and retroelements Rex1 and SINE) of mitotic chromosomes of Amazonian species of teiids (Ameiva ameiva, Cnemidophorus sp. 1, Kentropyx calcarata, Kentropyx pelviceps, and Tupinambis teguixin) to understand their genome organization and karyotype evolution. The mapping of repetitive sequences revealed a distinct pattern in Cnemidophorus sp. 1, whereas the other species showed all sequences interspersed in the heterochromatic region. Physical mapping of the tropomyosin 1 gene was performed for the first time in lizards and showed that in addition to being functional, this gene has a structural function similar to the mapped repetitive elements as it is located preferentially in centromeric regions and termini of chromosomes.

The organization and mapping of multigene families can produce useful genetic markers, and its use may elucidate the mechanisms of karyotype variation and genomic organization in different groups of eukaryotes. To date, few species of Coleoptera have been analyzed using FISH for the location of multigene families. The purpose of this study was to use high-resolution chromosome mapping to establish the genomic organization of the 18S rDNA, 5S rDNA and histone H3 gene families in Lagria villosa. FISH was performed using 18S rDNA, 5S rDNA and histone H3 probes prepared via PCR labeling. Fiber-FISH for 18S and 5S rDNA indicated that both ribosomal elements are colocalized in the short arm of chromosome 4. Additionally, FISH, using the histone H3 probe, revealed that this sequence is found in only one autosomal pair and did not colocalize with rDNA. Fiber-FISH with 5S and 18S probes, used to improve the mapping resolution of these regions, showed that both genes are closely interspersed with varying amounts of both DNA classes.

AA Amazônia Central possui a maior biodiversidade de espécies, sendo a ordem Coleoptera o maior grupo taxonômico dos animais. Para a citogenética de besouros, a presença de cromossomos sexuais gigantes e assinápticos, durante a meiose I, é uma característica marcante na tribo Alticini. O objetivo do trabalho foi realizar uma descrição citogenética de Omophoita abreviata (F., 1798), e Walterianella sp. utilizando coloração convencional e bandeamento C. Em ambos, foi encontrado o número diploide de 2n=22=20+X+Y com fórmula cariotípica 2n=10II+XY. A morfologia cromossômica variou, sendo predominantemente metacêntrica para O. abreviata, e submetacêntrica para Walterianella sp. Quanto aos cromossomos sexuais, O. abreviata possui morfologia submetacêntrica para o X e Y, em Walterianella sp. o X é metacêntrico e o Y é submetacêntrico com uma constrição secundária no braço longo. É descrito na literatura que o sistema X+Y da subtribo Oedionychina é o resultado de uma diferenciação gradual do sistema XYp com possíveis alterações cromossômicas como a perda do cromossomo y, translocações autossômicas para os cromossomos sexuais, inversões pericêntricas e alteração na quantidade de heterocromatina constitutiva. O estudo de células meióticas e mitóticas submetidas à técnica de Banda C mostrou a presença de um bloco heterocromático nas regiões centroméricas de cinco bivalentes autossômicos e para o cromossomo Y de O. abreviata. Para Walterianella sp. todos os bivalentes apresentam marcações na região centromérica, além de cinco marcações adicionais no braço longo do cromossomo y. Os resultados são inéditos para essas espécies de Alticini no ambiente amazônico, além de aumentar a compreensão sobre a evolução cariotípica do grupo.

Alticinae has the greatest amount of biodiversity among the Chrysomelidae, with 40,000 described species, only 290 of which have been analyzed cytogenetically. The majority of studies refer to conventional staining and few species have been analyzed or have responded to differential staining methods. The aim of the present study was to describe an 18S rDNA probe for Alticinae and the location of this cluster in species of the Omophoita genus. The fragment of approximately 750 bp obtained through a PCR (Polymerase Chain Reaction) amplification reaction with specific oligonucleotides to 18S rDNA was cloned and denominated pTZ_Ooct_18Sp and then submitted to automatic sequencing. The alignment of the sequences obtained through the sequencing of the clones generated a consensus sequence of 722 bp for Omophoita octoguttata with 98% homology with other species of Alticinae. The analysis of mitotic cells of O. octoguttata and Omophoita magniguttis submitted to fluorescent in situ hybridization (FISH) with the 18S rDNA probe revealed that the ribosomal genes are located in 6th pair. O. magniguttis also has a second labeled pair. Omophoita personata exhibited nucleolar organizer regions associated to one autosome pair. The analysis of meiotic cells submitted to FISH revealed one labeled bivalent in metaphase I in O. octoguttata and O. personata and in one chromosome in metaphase II in O. octoguttata . FISH data suggest a conserved pattern in the species analyzed and an apomorphy of O. magniguttis karyotype. The rDNA 18S probe could be considered an important marker to evidence the karyotypic differentiation, not observed with conventional methodologies, in species considered karyotypically conserved and uniform.

Background: B chromosomes, also known as supernumerary or accessory chromosomes, are additional chromosomes over the standard complement found in various groups of plants and animals. We investigated the presence of, and characterized, supernumerary microchromosomes in Astyanax goyacensis using classical and molecular cytogenetic methods. Findings: Three specimens possessed 2n = 50 chromosomes (8m + 26sm + 8st + 8a), and two specimens contained 1 to 9 additional B microchromosomes varying intra- and inter-individually. Chromosome painting with a B chromosome-specific probe yielded signals for several B microchromosomes, with one exhibiting no markings. Acrocentric chromosomes of the standard complement were also painted. Fluorescence in situ hybridization (FISH) using ribosomal probes located two chromosome pairs carrying 18S rDNA marked on the short arm, and one pair carrying 5S rDNA with pericentromeric markings. One chromosome was observed in synteny with 18S cistrons. Conclusion: These data contribute to knowledge of the karyotype evolution, the origin of B chromosomes, and to an understanding of the functionality of rDNA.