Chromosomal rearrangements are fundamental evolutionary drivers leading to genomic diversification. African clawed frogs (genus Xenopus, subgenera Silurana and Xenopus) represent an allopolyploid model system with conserved chromosome numbers in species with the same ploidy within each subgenus. Two significant interchromosomal rearrangements have been identified: a translocation between chromosomes 9 and 2, found in subgenus Silurana, and a fusion between chromosomes 9 and 10, probably widespread in subgenus Xenopus. Here, we study the allotetraploid Xenopus pygmaeus (subgenus Xenopus) based on in-depth karyotype analysis using chromosome measurements and fluorescent in situ hybridization (FISH). We designed FISH probes for genes associated with translocation and fusion to test for the presence of the two main types of rearrangements. We also examined the locations of 5S and 28S ribosomal tandem repeats, with the former often associated with telomeric regions and the latter with nucleolus organizer regions (NORs). The translocation-associated gene mapping did not detect the translocation in X. pygmaeus, supporting the hypothesis that the translocation is restricted to Silurana, but instead identified a pericentromeric inversion on chromosome 2S. The fusion-associated gene mapping confirmed the fusion of chromosomes 9 and 10, supporting this fusion as an ancestral state in subgenus Xenopus. As expected, the 5S repeats were found predominantly in telomere regions on almost all chromosomes. The nucleolar 28S repeats were localized on chromosome 6S, a position previously found only in the closely related species X. parafraseri, whereas other, phylogenetically more distant species have NORs located on different chromosomes. We therefore hypothesize that a jumping mechanism could explain the relatively frequent changes in the location of NORs during Xenopus evolution.

• MeSH
• Genome MeSH
• Gene Rearrangement * MeSH
• In Situ Hybridization, Fluorescence MeSH
• Karyotype MeSH
• Karyotyping MeSH
• Chromosome Mapping MeSH
• Evolution, Molecular MeSH
• Nucleolus Organizer Region * genetics   MeSH
• Translocation, Genetic MeSH
• Xenopus * genetics   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH

The genus Vigna (Leguminosae) comprises about 150 species grouped into five subgenera. The present study aimed to improve the understanding of karyotype diversity and evolution in Vigna, using new and previously published data through different cytogenetic and DNA content approaches. In the Vigna subgenera, we observed a random distribution of rDNA patterns. The 35S rDNA varied in position, from terminal to proximal, and in number, ranging from one (V. aconitifolia, V. subg. Ceratotropis) to seven pairs (V. unguiculata subsp. unguiculata, V. subg. Vigna). On the other hand, the number of 5S rDNA was conserved (one or two pairs), except for V. radiata (V. subg. Ceratotropis), which had three pairs. Genome size was relatively conserved within the genus, ranging from 1C = 0.43 to 0.70 pg in V. oblongifolia and V. unguiculata subsp. unguiculata, respectively, both belonging to V. subg. Vigna. However, we observed a positive correlation between DNA content and the number of 35S rDNA sites. In addition, data from chromosome-specific BAC-FISH suggest that the ancestral 35S rDNA locus is conserved on chromosome 6 within Vigna. Considering the rapid diversification in the number and position of rDNA sites, such conservation is surprising and suggests that additional sites may have spread out from this ancestral locus.

• Keywords
• Vigna, DNA content, FISH, Karyotype evolution, Molecular cytogenetics, rDNA sites,
• MeSH
• Chromosomes, Plant genetics   MeSH
• DNA, Plant genetics   MeSH
• Fabaceae genetics   MeSH
• Phylogeny MeSH
• Genetic Variation MeSH
• Karyotype MeSH
• DNA, Ribosomal genetics   MeSH
• Vigna * genetics   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• DNA, Plant MeSH
• DNA, Ribosomal MeSH

Fishes of the genus Carassius are useful experimental vertebrate models for the study of evolutionary biology and cytogenetics. Carassius demonstrates diverse biological characteristics, such as variation in ploidy levels and chromosome numbers, and presence of microchromosomes. Those Carassius polyploids with ≥150 chromosomes have microchromosomes, but the origin of microchromosomes, especially in European populations, is unknown. We used cytogenetics to study evolution of tandem repeats (U1 and U2 small nuclear DNAs and H3 histone) and microchromosomes in Carassius from the Czech Republic. We tested the hypotheses whether the number of tandem repeats was affected by polyploidization or divergence between species and what mechanism drives evolution of microchromosomes. Tandem repeats were found in tetraploid and hexaploid Carassius gibelio, and tetraploid Carassius auratus and Carassius carassius in conserved numbers, with the exception of U1 small nuclear DNA in C. auratus. This conservation indicates reduction and/or loss in the number of copies per locus in hexaploids and may have occurred by divergence rather than polyploidization. To study the evolution of microchromosomes, we used the whole microchromosome painting probe from hexaploid C. gibelio and hybridized it to tetraploid and hexaploid C. gibelio, and tetraploid C. auratus and C. carassius. Our results revealed variation in the number of microchromosomes in hexaploids and indicated that the evolution of the Carassius karyotype is governed by macrochromosome fissions followed by segmental duplication in pericentromeric areas. These are potential mechanisms responsible for the presence of microchromosomes in Carassius hexaploids. Differential efficacy of one or both of these mechanisms in different tetraploids could ensure variability in chromosome number in polyploids in general.

• Keywords
• FISH, U1 and U2 snDNAs, chromosome painting, histone H3, polyploidy, teleost fish,
• MeSH
• Cyprinidae * MeSH
• Cytogenetic Analysis MeSH
• Polyploidy MeSH
• Segmental Duplications, Genomic * MeSH
• Tandem Repeat Sequences MeSH
• Tetraploidy MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH