Pericentromeric Position Research Articles

The genomic study of repetitive elements in Solea senegalensis reveals multiple impacts of transposable elements in the evolution and architecture of Pleuronectiformes chromosomes

Pleuronectiformes are flatfishes with high commercial value and a prominent example of successful marine adaptation through chromosomal evolution. Hence, the aim of this study was to analyze the 14 relative abundance of repetitive elements (satellite DNA and transposable elements (TE)) in the 15 genome of 10 fish species (8 flatfish) delving into the study of the species of special relevance, 16 Senegalese sole, Solea senegalensis. The results showed differences in the abundance of repetitive elements, with S. senegalensis exhibiting the highest frequency and coverage of these elements reaching the 40% of the genome and not at random distribution. It is noteworthy the presence of relevant peaks of Helitrons in centromeric/pericentromeric positions mainly in the bi-armed chromosomes 1, 2, 4, 6, 7, and 9. The position of the centromeres of this species determined through the genomic localization of the family of satellite DNA PvuII, and other repetitive sequences was obtained de novo. This allowed us to know the genomic position of the centromeres in 19 out of the 21 chromosomes of S. senegalensis. Helitrons showed an accumulation of tandem copies mainly in the pericentromeric positions of chromosomes 1 and 2, occupying a region, in the first case, of 600Kb of tandem repeats. That has only been previously described in mammals and plants. Divergence and copy number studies indicated the presence of active families in the species’ genome and the existence of two important events of transposon activity (burst) in the genome of S. senegalensis, mainly accentuated in Helitrons. The results showed that only the families of DNA transposons exhibited a landscape with symmetrical bell-shaped distribution. The phylogenetic analysis of Helitron families revealed the presence of two large groups of families and the presence of four groups of sequences with heterogeneous distribution among chromosomes. Finally, the phylogenomic analysis of 8615 sequences belonging to Helitron insertions from 5 families of flatfish and two external species, allowed to classify the copies into nine groups of sequences with different levels of divergence and clusters, including some branches with distant phylogenetically species. The implications of this study will help to expand the knowledge of chromosome structure and evolution of these species.

Cytogenetics of four foam-nesting frog species of the Physalaemus gracilis group (Anura, Leptodactylidae)

Intending to increase the knowledge about cytogenetics of Physalaemus and the sparsely studied P. gracilis group, we analyzed the karyotypes of P. carrizorum, P. gracilis, P. lisei, and P. sp. aff. gracilis. We studied chromosome morphology, heterochromatin patterns, Ag-NORs location and mapped the repetitive DNA sequence PcP190. All species showed diploid karyotypes composed of 22 bi-armed chromosomes and similar C- bands and Ag-NOR patterns. C-bands were mainly centromeric and pericentromeric; non-centromeric C-bands were detected on the telomeres of pair 1 in P. lisei, although polymorphic, and interstitially on pair 10 of P. gracilis. This last character is useful to distinguish P. gracilis from its sibling species P. sp. aff. gracilis. The Ag-NOR sites were detected on the long arms of chromosome pair 8 but with a variable position among species. Clusters of PcP190 showed centromeric and pericentromeric positions coincident with conspicuous C-bands, on pairs 2 and 9 in P. gracilis and P. sp. aff. gracilis, pair 3 in P. carrizorum, and pair 7 in P. lisei. These results significantly increase the knowledge about Physalaemus cytogenetics and encourage further studies on the satellite PcP190 in other genera of Leiuperinae to better understand its taxonomic distribution and the evolutionary dynamics.

Karyotype Record for the Morphologically Derived, Rarely Collected, Freshwater Fish Ellopostoma mystax (Cypriniformes, Cobitoidea, Ellopostomatidae)

Freshwater fishes of the superfamily Cobitoidea are a species-rich group that are present in virtually every river in Europe and Asia. Three of the nine recognized families show massive karyotype reconstructions, including several independent cases of polyploidy, indicating cytogenetic evolution correlated with their diversification. We herein present the karyotype of a member of the monogeneric family Ellopostomatidae, a very rarely collected and morphologically highly enigmatic Southeast Asian representative of the Cobitoidea. The analyzed specimen of Ellopostoma mystax from southern Thailand had a diploid chromosome number of 2n = 48, with karyotype composed of three pairs of metacentric (m), 19 pairs of submeta- to subtelocentric (sm, st), and two pairs of acrocentric (a) chromosomes. Six pairs of sm to st chromosomes bore CMA3-positive sites either in pericentromeric positions or formed CMA3-positive p arms of the carrier chromosomes. Nucleolar organizing regions (NORs) as visualized by silver (Ag) impregnation were situated on the entire length of the shorter arms of the second largest sm to st pair of chromosomes; these corresponding sites also stained CMA3-positive. When compared with other families of Cobitoidea, the karyotype of Ellopostoma reveals a rather plesiomorphic composition, suggesting that the strong derivation of Ellopostoma based on morphology only was not accompanied by a cytogenetic derivation.

B Chromosomes and Cytogenetic Characteristics of the Common Nase Chondrostoma nasus (Linnaeus, 1758).

Supernumerary B chromosomes (Bs) are very promising structures, among others, in that they are an additional genomic compartment for evolution. In this study, we tested the presence and frequency of B chromosomes and performed the first cytogenetic examination of the common nase (Chondrostoma nasus). We investigated the individuals from two populations in the Vistula River basin, in Poland, according to the chromosomal distribution of the C-bands and silver nucleolar organizer regions (Ag-NORs), using sequential staining with AgNO3 and chromomycin A3 (CMA3). Furthermore, we analyzed the chromosomal localization of two rDNA families (45S and 5S rDNA) using fluorescence in situ hybridization (FISH) with rDNA probes. Chondrostoma nasus individuals showed a standard (A) chromosome set consisting of 2n = 50: 12 metacentric, 32 submetacentric, and 6 acrocentric chromosomes (NF = 94). Fourteen out of the 20 analyzed individuals showed 1–2 mitotically unstable submetacentric B chromosomes of different sizes. Six of them, in 14.1% of the analyzed metaphase plates, had a single, medium-sized submetacentric B (Bsm) chromosome (2n = 51) with a heterochromatic block located in its pericentromeric region. The other seven individuals possessed a Bsm (2n = 51) in 19.4% of the analyzed metaphase plates, and a second Bsm chromosome (2n = 52), the smallest in the set, in 15.5% of metaphase plates, whereas one female was characterized by both Bsm chromosomes (2n = 52) in 14.3% of the analyzed metaphase plates. AgNORs, GC-rich DNA sites, and 28S rDNA hybridization sites were observed in the short arms of two submetacentric chromosome pairs of A set. The constitutive heterochromatin was visible as C bands in the centromeric regions of almost all Chondrostoma nasus chromosomes and in the pericentromeric region of several chromosome pairs. Two 5S rDNA hybridization sites in the pericentromeric position of the largest acrocentric chromosome pair were observed, whereas two other such sites in co-localization on a smaller pair of NOR chromosomes indicate a species-specific character. The results herein broaden our knowledge in the field of B chromosome distribution and molecular cytogenetics of Chondrostoma nasus: a freshwater species from the Leuciscidae family.

Epigenetic analysis of high and low motile sperm populations reveals methylation variation in satellite regions within the pericentromeric position and in genes functionally related to sperm DNA organization and maintenance in Bos taurus

BackgroundSperm epigenetics is an emerging area of study supported by observations reporting that abnormal sperm DNA methylation patterns are associated with infertility. Here, we explore cytosine-guanine dinucleotides (CpGs) methylation in high (HM) and low motile (LM) Bos taurus sperm populations separated by Percoll gradient. HM and LM methylation patterns were investigated by bisulfite sequencing.ResultsComparison between HM and LM sperm populations revealed that methylation variation affects genes involved in chromatin organization. CpG Islands (CGIs), were highly remodelled. A high proportion of CGIs was found to be methylated at low/intermediate level (20–60%) and associated to the repetitive element BTSAT4 satellite. The low/intermediate level of methylation in BTSAT4 was stably maintained in pericentric regions of chromosomes. BTSAT4 was hypomethylated in HM sperm populations.ConclusionsThe characterization of the epigenome in HM and LM Bos taurus sperm populations provides a first step towards the understanding of the effect of methylation on sperm fertility. Methylation variation observed in HM and LM populations in genes associated to DNA structure remodelling as well as in a repetitive element in pericentric regions suggests that maintenance of chromosome structure through epigenetic regulation is probably crucial for correct sperm functionality.

Cytogenetics of tuna in Argentina (two forms of Opuntia ficus-indica (L.) Mill. and O. robusta J. C. Wendl., Cactaceae)

Opuntia ficus-indica (L.) Mill. f. ficus-indica (yellow tuna, cordobesa orange tuna, italiana orange tuna, saltena tuna) and f. amyclaea (white tuna, reddish tuna) and O. robusta J. C. Wendl. (cuaresma tuna) are extensively cultivated cacti in Argentina, mainly used as fodder and human food. Despite the importance of these resources, no studies of molecular cytogenetics considering the morphological characteristics of the varieties have been carried out. The main goal of this contribution is to determine the chromosome number, physical localization of ribosomal genes and amount of DNA in these taxa, including several populations with different fruit colors. The f. ficus-indica samples were octoploid, f. amyclaea hexaploid, and O. rubusta tetraploid. All taxa exhibited small similar-sized symmetrical chromosomes. Karyotypes were symmetrical with slight variations within each species. The 18S–5.8S–26S sites in all taxa were located on the secondary constrictions and the adjacent satellites at telomeric positions. The f. ficus-indica presented four 18S–5.8S–26S rDNA sites and the f. amyclaea three, whereas O. robusta had two. There were eight and six 5S rDNA sites in f. ficus-indica and f. amyclaea, respectively, and four in O. robusta. They were always proximally located on short arms of different chromosome pairs, always in a pericentromeric position. Both ribosomal genes were always asynthenic. The nuclear DNA in the octoploid f. ficus-indica presented a lower value (1Cx = 0.91 pg) than the hexaploid f.amyclaea (1Cx = 1.06 pg), whereas the tetraploid O. robusta had 1Cx = 0.87 pg. This cytogenetic evaluation is important for developing more efficient and faster selection strategies, contributing to obtaining new and improved varieties.

Comparative karyotype analysis among cytotypes of Cynodon dactylon (L.) Pers. (Poaceae).

Cynodon dactylon is characterized by taxonomic and systematic complexity, and polyploidy is one of the factors responsible for its genetic and morphological diversity. The aim of the present study was to compare karyotypes of C. dactylon cytotypes based on fluorescent banding and nuclear DNA content. The nine C. dactylon accessions evaluated were obtained from the Active Germplasm Bank (BAG) of the United States Department of Agriculture (USDA). Roots were pretreated with cycloheximide, fixed in Carnoy'ssolution and subjected to enzymatic digestion. Slides were prepared by the dissociation and air-drying technique. The fluorescent banding pattern was obtained using chromomycin A3 (CMA)/4,6-dimidino-2-phenylindole (DAPI) staining and DNA content was estimated by flow cytometry. The chromosome number of the accessions ranged from 2n = 2x = 18 to 2n = 5x = 45. Chromosomal polymorphism was observed based on the distribution and number of heterochromatic bands, with CMA+ bands located in the pericentromeric position and DAPI+ bands mainly in the terminal position. PI477004-26 (2n = 3x = 27) and PI291966-27 (2n = 4x = 36) had the highest and lowest number of DAPI+ bands, respectively. The number of CMA+ bands was stable, as only PI477004-26, PI291966-27 and PI289750-10 (2n = 5x = 45) showed variation. There was no direct correlation between an increase in the ploidy level and an increase in the percentage of heterochromatic regions, mainly in relation to A-T-richblocks. The chromosomal banding variation found reinforces the notion of allopolyploidy occurrence in C. dactylon and demonstrates the genomic complexity of this species regard to repetitive DNA content.

TIR-Learner, a New Ensemble Method for TIR Transposable Element Annotation, Provides Evidence for Abundant New Transposable Elements in the Maize Genome

Transposable elements (TEs) make up a large and rapidly evolving proportion of plant genomes. Among Class II DNA TEs, TIR elements are flanked by characteristic terminal inverted repeat sequences (TIRs). TIR TEs may play important roles in genome evolution, including generating allelic diversity, inducing structural variation, and regulating gene expression. However, TIR TE identification and annotation has been hampered by the lack of effective tools, resulting in erroneous TE annotations and a significant underestimation of the proportion of TIR elements in the maize genome. This problem has largely limited our understanding of the impact of TIR elements on plant genome structure and evolution. In this paper, we propose a new method of TIR element detection and annotation. This new pipeline combines the advantages of current homology-based annotation methods with powerful de novo machine-learning approaches, resulting in greatly increased efficiency and accuracy of TIR element annotation. The results show that the copy number and genome proportion of TIR elements in maize is much larger than that of current annotations. In addition, the distribution of some TIR superfamily elements is reduced in centromeric and pericentromeric positions, while others do not show a similar bias. Finally, the incorporation of machine-learning techniques has enabled the identification of large numbers of new DTA (hAT) family elements, which have all the hallmarks of bona fide TEs yet which lack high homology with currently known DTA elements. Together, these results provide new tools for TE research and new insight into the impact of TIR elements on maize genome diversity.

A comparative cytogenetic study of 17 Avena species using Am1 and (GAA)6 oligonucleotide FISH probes

Fluorescence in situ hybridization (FISH) was performed to explore the genomic and species relationships among 17 taxa using Am1 (oligo-Am1) and (GAA)6 oligonucleotide probes. Oligo-Am1 (51 bp) hybridized strongly over almost the entire length of all chromosomes in the C genome. Six translocations between the A and C genomes were found in AACC tetraploids and AACCDD hexaploids, four minor translocations between the C and D genomes were found in AACCDD hexaploids, and two large translocations between the C and D genomes were found in A. sativa. In the 17 Avena species, (GAA)6 regions mainly appear as sharp, thin bands at pericentromeric positions in the A, B, and C genomes and at termini in the B genome. However, no (GAA)6 signal loci were observed in the D genome. The (GAA)6 signal number was constant in both AA and CC diploids, though with different signal intensities. The (GAA)6 signal pattern was diverse in AABB, AACC, and AACCDD polyploids, with each species exhibiting one signal pattern. The (GAA)6 signal number was consistent in diploids and varied in polyploids, describing an intragenomic relationship among Avena species. This study is the first to test these two oligonucleotides, which are based on synthesized repeat units (18–51 bp), in the genus Avena. Our approach paves the way for future studies in which FISH probes can be used to assign other landmark genomic sequence oligonucleotides to physical chromosomes.

Evolutionary trends in animal ribosomal DNA loci: introduction to a new online database

Ribosomal DNA (rDNA) loci encoding 5S and 45S (18S-5.8S-28S) rRNAs are important components of eukaryotic chromosomes. Here, we set up the animal rDNA database containing cytogenetic information about these loci in 1343 animal species (264 families) collected from 542 publications. The data are based on in situ hybridisation studies (both radioactive and fluorescent) carried out in major groups of vertebrates (fish, reptiles, amphibians, birds, and mammals) and invertebrates (mostly insects and mollusks). The database is accessible online at www.animalrdnadatabase.com. The median number of 45S and 5S sites was close to two per diploid chromosome set for both rDNAs despite large variation (1–74 for 5S and 1–54 for 45S sites). No significant correlation between the number of 5S and 45S rDNA loci was observed, suggesting that their distribution and amplification across the chromosomes follow independent evolutionary trajectories. Each group, irrespective of taxonomic classification, contained rDNA sites at any chromosome location. However, the distal and pericentromeric positions were the most prevalent (> 75% karyotypes) for 45S loci, while the position of 5S loci was more variable. We also examined potential relationships between molecular attributes of rDNA (homogenisation and expression) and cytogenetic parameters such as rDNA positions, chromosome number, and morphology.

The Diversity of Sequence and Chromosomal Distribution of New Transposable Element-Related Segments in the Rye Genome Revealed by FISH and Lineage Annotation.

Transposable elements (TEs) in plant genomes exhibit a great variety of structure, sequence content and copy number, making them important drivers for species diversity and genome evolution. Even though a genome-wide statistic summary of TEs in rye has been obtained using high-throughput DNA sequencing technology, the accurate diversity of TEs in rye, as well as their chromosomal distribution and evolution, remains elusive due to the repetitive sequence assembling problems and the high dynamic and nested nature of TEs. In this study, using genomic plasmid library construction combined with dot-blot hybridization and fluorescence in situ hybridization (FISH) analysis, we successfully isolated 70 unique FISH-positive TE-related sequences including 47 rye genome specific ones: 30 showed homology or partial homology with previously FISH characterized sequences and 40 have not been characterized. Among the 70 sequences, 48 sequences carried Ty3/gypsy-derived segments, 7 sequences carried Ty1/copia-derived segments and 15 sequences carried segments homologous with multiple TE families. 26 TE lineages were found in the 70 sequences, and among these lineages, Wilma was found in sequences dispersed in all chromosome regions except telomeric positions; Abiba was found in sequences predominantly located at pericentromeric and centromeric positions; Wis, Carmilla, and Inga were found in sequences displaying signals dispersed from distal regions toward pericentromeric positions; except DNA transposon lineages, all the other lineages were found in sequences displaying signals dispersed from proximal regions toward distal regions. A high percentage (21.4%) of chimeric sequences were identified in this study and their high abundance in rye genome suggested that new TEs might form through recombination and nested transposition. Our results also gave proofs that diverse TE lineages were arranged at centromeric and pericentromeric positions in rye, and lineages like Abiba might play a role in their structural organization and function. All these results might help in understanding the diversity and evolution of TEs in rye, as well as their driving forces in rye genome organization and evolution.

An uncommon co-localization of rDNA 5S with major rDNA clusters in Callichthyidae (Siluriformes): a report case in Corydoras carlae Nijssen & Isbrücker, 1983.

Corydoras Lacepède, 1803 is the most specious genus of Corydoradinae subfamily and many of its species are still unknown in relation to molecular cytogenetic markers. However, the diploid number and karyotypic formula were recorded for many species of this group. In current study, we provided the first cytogenetic information of Corydoras carlae Nijssen & Isbrücker, 1983, an endemic fish species from Iguassu River basin, Paraná State, Brazil. The individuals were collected in Florido River, a tributary of Iguassu River and analysed with respect to diploid number, heterochromatin distribution pattern, Ag-NORs and mapping of 5S and 18S ribosomal genes. The karyotype of this species comprises 46 chromosomes arranged in 22m+22sm+2st. The heterochromatin is distributed in centromeric and pericentromeric positions in most of the chromosomes, and also associated with NORs. The Ag-NORs were detected in the terminal position on the long arm of the metacentric pair 6. The double-FISH technique showed that 5S rDNA and 18S rDNA were co-localized in the terminal portion on the long arm of the metacentric pair 6. This condition of co-localization of ribosomal genes in Corydoras carlae seems to represent a marker for this species.

Cytogenetic Analysis of Lilium rosthornii

Lily (Lilium L.) species produce among the most important cut flowers worldwide. China has ≈55 species of Lilium. Although many plants from this genus have been used in hybridization efforts, their cytology has remained unclear. The goal of the current study was to characterize the chromosomes of Lilium rosthornii Diels. Root tips were used to characterize Giemsa C-banding, propidium iodide (PI) banding, and 45S rDNA locations. The karyotype of L. rosthornii belongs to type 3B. C-banding revealed polymorphic banding patterns with the following formula: 2n = 24 = CI = 4C + 14CI+ + 2I+ +2I+ 2. Two of the four 45S rDNA hybridization sites were located at pericentromeric positions on the two short arms of the homologues of chromosome 1, and the other two were located on the long arms of one chromosome 6 homolog and one chromosome 11 homolog. Six of the eight PI bands were detected in the centromeres of the homologues of chromosomes 1, 5, and 8, and the other two PI bands were detected on the long arms of one chromosome 6 and one chromosome 11. Lilium rosthornii showed enriched banding in both Giemsa C-banding and PI painting. Interestingly, not all 45S rDNA was located in homologous chromosomal locations. These results may provide reference data for L. rosthornii for use in further Lilium breeding.

Comparative Cytogenetics of Hoplerythrinus unitaeniatus (Agassiz, 1829) (Characiformes, Erythrinidae) Species Complex from Different Brazilian Hydrographic Basins

Chromosomal characteristics of Hoplerythrinus unitaeniatus populations from 5 Brazilian river basins, namely Arinos (Amazonas basin), Araguaia, Paraguai, Alto Paraná, and São Francisco were analyzed by conventional Giemsa staining, C-banding, silver nitrate impregnation, and fluorescence in situ hybridization (FISH) with 18S and 5S rDNA and telomeric sequence (TTAGGG)_n probes. The diploid chromosome number was 2n = 48 in representatives of the populations from Paraguai and Alto Paraná River basins and 2n = 52 for those from the Arinos and Araguaia River basins. The São Francisco population had individuals with 2n = 50 and 52 occurring in sympatry. C-banding showed heterochromatic blocks mainly located at interstitial and pericentromeric positions in most of the chromosomes. Silver nitrate impregnation demonstrated simple NORs for representatives from Arinos and Araguaia River populations and multiple NORs for specimens from Paraguai, Alto Paraná, and São Francisco River populations. FISH with 18S and 5S rDNA probes revealed many chromosomes carrying these cistrons, with up to 21 chromosomes bearing 18S rDNA sites (Alto Rio Paraná basin) and up to 12 chromosomes with 5S rDNA sites (Paraguai basin), besides the occurrence of colocalization in all populations. FISH with telomeric sequence (TTAGGG)_n detected sites in the terminal portion of the chromosomes in all populations. These data reinforce the idea that H. unitaeniatus is a species complex. Evolutionary and biogeographical aspects of the group in the Neotropical region are discussed.

On the Origin and Evolution of the Extant System of B Chromosomes in Oryzomyini Radiation (Rodentia, Sigmodontinae).

Heterogeneous supernumerary chromosomes (Bs) are recognized in the oryzomyines Holochilus brasiliensis, Nectomys rattus, N. squamipes, Oligoryzomys flavescens and Sooretamys angouya, representing about 10% of all known B-containing rodent species. They provide an outstanding model for understanding the origin, evolution and diversity of Bs in a phylogenetic context. Therefore, whole chromosome-specific probes were generated from flow-sorted Holochilus brasiliensis (HBR) autosomes 11 and 25+26 and chromosomes X, Y and Bs. Hybridizations were performed on male metaphases of 15 Oryzomyini species of which 3 are B-containing species. The results reveal that among the species sampled, 12 of them, belonging to a monophyletic Oryzomiyini subclade, are positive for an anonymous Oryzomyini shared heterochromatic region (OSHR) on both sex chromosomes. The OSHR is also present on Bs of Holochilus brasiliensis, Nectomys rattus and N. squamipes but not on Bs of O. flavescens and S. angouya. Two distinct additional OSHR/autosome associations are observed on S. angouya. The three species that are OSHR negative belong to an outgroup. Molecular dating suggests that the OSHR originated between 7.8 and 3 Mya on ancestral sex chromosomes. A tentative explanation for the OSHR-positive nature of B regions in three species could be that transposable elements (TEs) from this specific sex chromosome region may have invaded existing B chromosomes. The presence of the OSHR on entire Xp and Yp adjacent to interstitial telomeric sequences at pericentromeric positions, as observed in Drymoreomys albimaculatus, show a similar organization as on B chromosomes in Nectomys squamipes. The diversity of the Oryzomyini Bs in number, size, morphology and genetic content may be explained by the independent origin of B chromosomes in different subgroups of species, with Bs in Holochilus brasiliensis, Nectomys squamipes and N. rattus sharing the OSHR with sex chromosomes, and those in Oligoryzomys flavescens and Sooretamys angouya lacking OSHR in Bs. The species-specific pattern of Bs is probably a consequence of their independent evolutionary origin.

Cytogenetics of <i>Trichomycterus brasiliensis</i> (Siluriformes: Trichomycteridae) from the Upper São Francisco River Basin (MG)

Summary Trichomycteridae is a family of small catfish which is widely distributed throughout Southern Central America and South America. Specimens of Trichomycterus brasiliensis collected in the upper Sao Francisco River Basin in Brasil were studied cytogenetically. All individuals presented 2n=54 chromosomes, including 34 metacentric, 18 submetacentric and 2 subtelocentric chromo somes. A secondary constriction was observed in the interstitial region of the short arm of the chromosome pair number 20, coinciding with the NOR and 18S rDNA. The first metacentric pair is considerably larger than the second metacentric pair and the NORs occur in the pericentromeric position of the short arm of a large submetacentric pair, allowing to place this species in one of the cis-Andean groups already identified of Trichomycterus.

Karyotype Patterns ofHypsolebias antenori(Cyprinodontiformes: Rivulidae): An Endangered Killifish of the Semiarid Region of Brazil

Annual fish which belong to the order Cyprinodontiformes constitute an excellent model for evolutionary studies. their short life cycle, distribution in ecologically dynamic environments, and low agility make them favorable for genetic analyses. The species Hypsolebias antenori (Rivulidae), encountered in seasonal pools located in the semiarid region of Northeastern Brazil, has been the object of surveys with a view to study its ecological and behavioral aspects. This study reports on the karyotype patterns of this species, which represents the first contribution to the cytogenetics of this genus. The karyotype of this species is composed of 2n = 48 chromosomes (6m + 4sm + 36st; NF = 96); the heterochromatic regions are located in centromeric or pericentromeric position and are more pronounced in the nucleolar organizer regions. Two sites Ag-NORs/CMA+/DAPI were identified in the short arms of pairs 2 (metacentric) and 21 (subtelocentric). Unlike the other species of this family which show an evolution modulated by events of centric fusions, H. antenori shows the maintenance of a basal diploid number and the large number of bibrachial elements indicates karyotypic diversification derived by pericentric inversions. Cytogenetic analyzes in this species will provide new taxonomic markers capable of being utilized in conservation issues and systematics.

The sex‐linked region in Populus tremuloides Turesson 141 corresponds to a pericentromeric region of about two million base pairs on P. trichocarpa chromosome 19

In the dioecious genus Populus, sex determination has been located to chromosome 19. However, despite a high degree of genome collinearity, various Populus species seem to differ with regard to the location of the sex-determining region on the respective chromosome and the apparent heterogametic sex. In this study, the boundaries of the recombination-suppressed, sex-linked region of the male P. tremuloides clone Turesson 141 were localised by genetic mapping using new SNP and InDel markers. The respective region seems to be located in a pericentromeric position. The corresponding P. trichocarpa genome region spans about two million bp and comprises 65 gene loci, which were bioinformatically evaluated for their potential as candidate genes for sex determination. Three putative transcription factor genes and four genes that are potentially involved in flower development processes, e.g. meristem transition from the vegetative to the reproductive phase, were identified. Populus tremuloides sequence data of the sex-linked region is required for a final search for candidate genes.

Characterization of two major satellite DNAs specific to the genus Discoglossus (Amphibia, Anura)

Two new high repetitive DNAs were isolated from Discoglossus pictus genomic DNA digested with StuI. Sequence analysis of clones indicated two types of repetitive units 143–148 bp and 170–177 bp long, respectively. Southern blot analyses show ladders of bands indicating that both repetitive units are organized in long tandem arrays and belong to two different satellite DNAs that were named Dp-sat2 and Dp-sat3. A similar ladder of bands was also produced when genomic DNA was digested with ClaI in the case of Dp-sat2, or with ScaI in the case of Dp-sat3. Quantitative dot-blot analyses indicate that Dp-sat2 and Dp-sat3 account for about 2.6% and 2.2%, respectively, of the D. pictus genome. Considering that D. pictus has a genomic DNA content of 10.5 pg/N, our data indicate that Dp-sat2 and Dp-sat3 repetitive units are present in about 2.3×106 and 1.6×106 copies per diploid genome, respectively. Dp-sat2 and Dp-sat3 probes produced the same patterns of hybrid bands in Southern blots and the same genomic content in dot-blots in all the other Discoglossus species, except D. montalentii which showed a different band pattern and genomic content. The chromosomal distribution of the two StuI satellites shows some similarities: both Dp-sat2 and Dp-sat3 probes mainly labelled the pericentromeric regions of the large chromosome pairs 1–5 and 7. Moreover, probes from both satellite DNAs also produced faint fluorescent mini-spots along almost all chromosome pairs. These data suggest that both satellite DNAs have two types of organization, one in long arrays localized in pericentromeric positions, and the other in short arrays dispersed in the genome.

Karyotype of the Bird Blowfly, Protocalliphora falcozi Séguy, 1928 (Diptera, Calliphoridae)

The karyotype structure of Protocalliphora falcozi is described for the first time. The diploid complement comprises 2n = 12, n(male) = 5+XY. Male mitotic plates include four pairs of long (metacentric) and one pair of medium-sized (submetacentric) autosomes. The submetacentric sex chromosomes X and Y are the smallest elements of the set. An achiasmatic meiosis was determined. The heterochromosomes do not form a heterovalent because they occur separately during the first meiotic division. The examined karyotype shows a pericentromeric position of constitutive heterochromatin in all autosomes. The longer arm of the X chromosome is heterochromatic, while the Y is entirely euchromatic. The NORs are active at mitotic prophase and at early meiotic stages. Small, bright signals were observed in the centromeric regions of autosomes after DAPI staining.