Sex chromosomes have evolved repeatedly across eukaryotes. The emergence of a sex-determining (SD) locus is expected to progressively restrict recombination, driving convergent molecular differentiation. However, evidence from taxa like teleost fishes, representing over half of vertebrate species with unmatched diversity in SD systems, challenges this model. Teleost sex chromosomes are often difficult to detect as they experience frequent turnovers, resetting the differentiation process. Nothobranchius killifishes, which include the XY system shared by N. furzeri and N. kadleci and X1X2Y systems in six other species, offer a valuable model to study sex chromosome turnovers. We characterised X1X2Y systems in five killifish species and found that sex chromosomes evolved at least four times independently. Sex-determining regions resided near centromeres or predicted chromosome rearrangement breakpoints in N. brieni and N. guentheri, suggesting recombination cold spots may facilitate sex chromosome evolution. Chromosomes representing the XY system in N. furzeri/N. kadleci were sex-linked also in the outgroup Fundulosoma thierryi, with several genes, including gdf6, residing in the region of differentiation. Although the X1X2Y systems of N. guentheri, N. lourensi (both Coastal clade), and N. brieni (Kalahari clade) involved different chromosomes, they shared a potential SD region. We uncovered two sex-linked evolutionary strata of distinct age in N. guentheri. However, its potential SD gene amhr2 was located in the younger stratum and is hence unlikely to be the ancestral SD gene in this lineage. Our findings suggest recombination landscapes shape sex chromosome turnover and that certain synteny blocks are repeatedly co-opted as sex chromosomes in killifishes.

• Klíčová slova
• bacterial artificial chromosome, chromosome fusion, pool‐seq, recombination suppression, sex chromosome differentiation, zoo‐FISH,
• MeSH
• Cyprinodontidae * genetika   MeSH
• fylogeneze MeSH
• molekulární evoluce * MeSH
• pohlavní chromozomy * genetika   MeSH
• procesy určující pohlaví * genetika   MeSH
• rekombinace genetická MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

BACKGROUND: Java combtail fish Belontia hasselti (Cuvier, 1831), a member of the Osphronemidae family, inhabits lakes and rivers throughout Southeast Asia and Sri Lanka. Previous cytogenetic research revealed it possesses a diploid chromosome number of 48 chromosomes with a female-heterogametic ZZ/ZW sex chromosome system, where the W chromosome is distinguishable as the only metacentric element in the complement. Female-heterogametic sex chromosome systems seem to be otherwise surprisingly rare in the highly diverse order Perciformes and, therefore, B. hasselti provides an important comparative model to evolutionary studies in this teleost lineage. To examine the level of sex chromosome differentiation in B. hasselti and the contribution of repetitive DNAs to this process we combined bioinformatic analyses with chromosomal mapping of selected repetitive DNA classes, and comparative genomic hybridization. RESULTS: By providing the first satellitome study in Perciformes, we herein identified 13 satellite DNA monomers in B. hasselti, suggesting a very low diversity of satDNA in this fish species. Using fluorescence in situ hybridization, we revealed detectable clusters on chromosomes only for four satellite DNA monomers. Together with the two mapped microsatellite motifs, the repeats primarily accumulated on autosomes, with no distinct clusters located on the sex chromosomes. Comparative genomic hybridization showed no region with accumulated female-specific or enriched repeats on the W chromosome. Telomeric repeats terminated all chromosomes, and no additional interstitial sites were detected. CONCLUSION: These data collectively indicate a low degree of sex chromosome differentiation in B. hasselti despite their considerable heteromorphy. Possible mechanisms that may underlie this pattern are discussed.

• Klíčová slova
• Fishes, Isochromosome, Molecular cytogenetics, Satellitome, Sex chromosome evolution, Teleostei,
• MeSH
• hybridizace in situ fluorescenční MeSH
• mapování chromozomů MeSH
• mikrosatelitní repetice MeSH
• Perciformes * genetika   MeSH
• pohlavní chromozomy * genetika   MeSH
• repetitivní sekvence nukleových kyselin * MeSH
• satelitní DNA genetika   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• satelitní DNA MeSH

Acanthocephalan parasites are often overlooked in many areas of research, and satellitome and cytogenetic analyzes are no exception. The species of the genus Acanthocephalus are known for their very small chromosomes with ambiguous morphology, which makes karyotyping difficult. In this study, we performed the first satellitome analysis of three Acanthocephalus species to identify species- and chromosome-specific satellites that could serve as cytogenetic markers. RepeatExplorer2 revealed a remarkably high number of species-specific repeats, with a predominance of satellite DNAs, alongside variations in repetitive content between sexes. Five satellites in A. anguillae, two in A. lucii and six in A. ranae were successfully mapped to chromosomes using FISH. Each satellite showed a clustered hybridization signal at specific chromosomal locations, which allowed us to create a schematic representation of the distribution of satellites for each species. These newly identified satellites proved to be useful chromosomal markers for the accurate identification of homologous chromosome pairs. No FISH-positive signals were observed on the supernumerary chromosomes of A. anguillae and A. lucii, supporting the hypothesis that these chromosomes have recent origin.

• Klíčová slova
• Acanthocephala, Fluorescence in situ hybridization, Repeat, RepeatExplorer2, Satellite DNA,
• MeSH
• Acanthocephala * genetika   klasifikace   MeSH
• chromozomy genetika   MeSH
• druhová specificita MeSH
• genetické markery MeSH
• hybridizace in situ fluorescenční MeSH
• karyotypizace MeSH
• satelitní DNA * genetika   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• genetické markery MeSH
• satelitní DNA * MeSH

Zoraptera (also called "angel insects") is one of the most unexplored insect orders. However, it holds promise for understanding the evolution of insect karyotypes and genome organization given its status as an early branching group of Polyneoptera and Pterygota (winged insects) during the Paleozoic. Here, we provide karyotype descriptions of three Zorapteran species: Brazilozoros huxleyi (2n♂; ♀ = 42; 42), B. kukalovae (2n♂; ♀ = 43; 44) and Latinozoros cacaoensis (2n♂; ♀ = 36; 36). These species represent two of the four recently recognized Zorapteran subfamilies. Contrary to an earlier suggestion that Zoraptera has holocentric chromosomes, we found karyotypes that were always monocentric. Interestingly, we detected both X0 (B. kukalovae) and XY (B. huxleyi, L. cacaoensis) sex chromosome systems. In addition to conventional karyotype descriptions, we applied fluorescent in situ hybridization for the first time in Zoraptera to map karyotype distributions of 18S rDNA, histone H3 genes, telomeres and (CAG)n and (GATA)n microsatellites. This study provides a foundation for cytogenetic research in Zoraptera.

• Klíčová slova
• Karyotype, Microsatellites, Sex chromosomes, Telomere, rDNA,
• MeSH
• chromozomy hmyzu * genetika   MeSH
• cytogenetika metody   MeSH
• histony genetika   MeSH
• hmyz genetika   klasifikace   MeSH
• hybridizace in situ fluorescenční MeSH
• karyotyp * MeSH
• mikrosatelitní repetice genetika   MeSH
• molekulární evoluce MeSH
• pohlavní chromozomy genetika   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• srovnávací studie MeSH
• Názvy látek
• histony MeSH

Multiple sex chromosomes usually arise from chromosomal rearrangements which involve ancestral sex chromosomes. There is a fundamental condition to be met for their long-term fixation: the meiosis must function, leading to the stability of the emerged system, mainly concerning the segregation of the sex multivalent. Here, we sought to analyze the degree of differentiation and meiotic pairing properties in the selected fish multiple sex chromosome system present in the wolf-fish Hoplias malabaricus (HMA). This species complex encompasses seven known karyotype forms (karyomorphs) where the karyomorph C (HMA-C) exhibits a nascent XY sex chromosomes from which the multiple X1X2Y system evolved in karyomorph HMA-D via a Y-autosome fusion. We combined genomic and cytogenetic approaches to analyze the satellite DNA (satDNA) content in the genome of HMA-D karyomorph and to investigate its potential contribution to X1X2Y sex chromosome differentiation. We revealed 56 satDNA monomers of which the majority was AT-rich and with repeat units longer than 100 bp. Seven out of 18 satDNA families chosen for chromosomal mapping by fluorescence in situ hybridization (FISH) formed detectable accumulation in at least one of the three sex chromosomes (X1, X2 and neo-Y). Nine satDNA monomers showed only two hybridization signals limited to HMA-D autosomes, and the two remaining ones provided no visible FISH signals. Out of seven satDNAs located on the HMA-D sex chromosomes, five mapped also to XY chromosomes of HMA-C. We showed that after the autosome-Y fusion event, the neo-Y chromosome has not substantially accumulated or eliminated satDNA sequences except for minor changes in the centromere-proximal region. Finally, based on the obtained FISHpatterns, we speculate on the possible contribution of satDNA to sex trivalent pairing and segregation.

• Klíčová slova
• FISH, Meiosis, Multiple sex chromosomes, Satellitome, Sex trivalent,
• MeSH
• Characiformes * genetika   MeSH
• chromozom Y genetika   MeSH
• hybridizace in situ fluorescenční * MeSH
• karyotyp MeSH
• meióza genetika   MeSH
• molekulární evoluce MeSH
• pohlavní chromozomy * genetika   MeSH
• satelitní DNA * genetika   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• satelitní DNA * MeSH