Although crocodilians have attracted enormous attention in other research fields, from the cytogenetic point of view, this group remains understudied. Here, we analyzed the karyotypes of eight species formally described from the Alligatoridae family using differential staining, fluorescence in situ hybridization with rDNA and repetitive motifs as a probe, whole chromosome painting (WCP), and comparative genome hybridization. All Caimaninae species have a diploid chromosome number (2n) 42 and karyotypes dominated by acrocentric chromosomes, in contrast to both species of Alligatorinae, which have 2n = 32 and karyotypes that are predominantly metacentric, suggesting fusion/fission rearrangements. Our WCP results supported this scenario by revealing the homeology of the largest metacentric pair present in both Alligator spp. with two smaller pairs of acrocentrics in Caimaninae species. The clusters of 18S rDNA were found on one chromosome pair in all species, except for Paleosuchus spp., which possessed three chromosome pairs bearing these sites. Similarly, comparative genomic hybridization demonstrated an advanced stage of sequence divergence among the caiman genomes, with Paleosuchus standing out as the most divergent. Thus, although Alligatoridae exhibited rather low species diversity and some level of karyotype stasis, their genomic content indicates that they are not as conserved as previously thought. These new data deepen the discussion of cytotaxonomy in this family.

• Klíčová slova
• Alligatoridae, chromosome, cytogenomics, molecular cytogenetics,
• MeSH
• aligátoři a krokodýli klasifikace   genetika   MeSH
• chromozomy genetika   MeSH
• hybridizace in situ fluorescenční MeSH
• karyotyp * MeSH
• molekulární evoluce * MeSH
• srovnávací genomová hybridizace MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The Asian box turtle genus Cuora currently comprises 13 species with a wide distribution in Southeast Asia, including China and the islands of Indonesia and Philippines. The populations of these species are rapidly declining due to human pressure, including pollution, habitat loss, and harvesting for food consumption. Notably, the IUCN Red List identifies almost all species of the genus Cuora as Endangered (EN) or Critically Endangered (CR). In this study, we explore the karyotypes of 10 Cuora species with conventional (Giemsa staining, C-banding, karyogram reconstruction) and molecular cytogenetic methods (in situ hybridization with probes for rDNA loci and telomeric repeats). Our study reveals a diploid chromosome number of 2n = 52 chromosomes in all studied species, with karyotypes of similar chromosomal morphology. In all examined species, rDNA loci are detected at a single medium-sized chromosome pair and the telomeric repeats are restricted to the expected terminal position across all chromosomes. In contrast to a previous report, sex chromosomes are neither detected in Cuoragalbinifrons nor in any other species. Therefore, we assume that these turtles have either environmental sex determination or genotypic sex determination with poorly differentiated sex chromosomes. The conservation of genome organization could explain the numerous observed cases of interspecific hybridization both within the genus Cuora and across geoemydid turtles.

• Klíčová slova
• C-banding, Cuora, FISH, Geoemydidae, evolution, heterochromatin, karyotype, microsatellites, rDNA, telomeres,
• MeSH
• cytogenetické vyšetření * MeSH
• fylogeneze MeSH
• hybridizace in situ fluorescenční MeSH
• karyotyp MeSH
• mikrosatelitní repetice MeSH
• molekulární evoluce MeSH
• pruhování chromozomů MeSH
• ribozomální DNA genetika   MeSH
• taxonomické DNA čárové kódování MeSH
• telomery MeSH
• želvy klasifikace   genetika   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• ribozomální DNA MeSH

Turtles demonstrate variability in sex determination and, hence, constitute an excellent model for the evolution of sex chromosomes. Notably, the sex determination of the freshwater turtles from the family Chelidae, a species-rich group with wide geographical distribution in the southern hemisphere, is still poorly explored. Here we documented the presence of an XX/XY sex determination system in seven species of the Australasian chelid genera Chelodina, Emydura, and Elseya by conventional (karyogram reconstruction, C-banding) and molecular cytogenetic methods (comparative genome hybridization, in situ hybridization with probes specific for GATA microsatellite motif, the rDNA loci, and the telomeric repeats). The sex chromosomes are microchromosomes in all examined species of the genus Chelodina. In contrast, the sex chromosomes are the 4th largest pair of macrochromosomes in the genera Emydura and Elseya. Their X chromosomes are submetacentric, while their Y chromosomes are metacentric. The chelid Y chromosomes contain a substantial male-specific genomic region with an accumulation of the GATA microsatellite motif, and occasionally, of the rDNA loci and telomeric repeats. Despite morphological differences between sex chromosomes, we conclude that male heterogamety was likely already present in the common ancestor of Chelodina, Emydura and Elseya in the Mesozoic period.

• MeSH
• chromozom X genetika   MeSH
• chromozom Y genetika   MeSH
• genom * MeSH
• karyotyp MeSH
• mikrosatelitní repetice MeSH
• molekulární evoluce * MeSH
• pohlavní chromozomy genetika   MeSH
• procesy určující pohlaví MeSH
• želvy MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

For a long time, turtles of the family Geoemydidae have been considered exceptional because representatives of this family were thought to possess a wide variety of sex determination systems. In the present study, we cytogenetically studied Geoemyda spengleri and G. japonica and re-examined the putative presence of sex chromosomes in Pangshura smithii. Karyotypes were examined by assessing the occurrence of constitutive heterochromatin, by comparative genome hybridization and in situ hybridization with repetitive motifs, which are often accumulated on differentiated sex chromosomes in reptiles. We found similar karyotypes, similar distributions of constitutive heterochromatin and a similar topology of tested repetitive motifs for all three species. We did not detect differentiated sex chromosomes in any of the species. For P. smithii, a ZZ/ZW sex determination system, with differentiated sex chromosomes, was described more than 40 years ago, but this finding has never been re-examined and was cited in all reviews of sex determination in reptiles. Here, we show that the identification of sex chromosomes in the original report was based on the erroneous pairing of chromosomes in the karyogram, causing over decades an error cascade regarding the inferences derived from the putative existence of female heterogamety in geoemydid turtles.

• Klíčová slova
• Comparative genome hybridization, Evolution, FISH, Karyotype, Microsatellite, Sex chromosomes, Sex determination, Telomeres, Turtles,
• Publikační typ
• časopisecké články MeSH