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Karyotypes and chromosomal locations of C-banded heterochromatin and silver-positive nucleolus organizer regions (Ag-NORs) were studied in two anemonefish species, Amphiprion ocellaris and A. ephippium. These two species had the same diploid chromosome number of 48 and the same fundamental number (NF) of 86. As a remarkable feature found in conventional stained chromosomes, A. ocellaris had distinct secondary constrictions (SCs) in the pericentromeric regions in the long arms of a pair of the large submetacentric chro-mosomes. The Ag-NOR staining revealed that these SCs were Ag-NORs. This interstitial type of NOR-location was first case in anemonefish species. On the other hand, Ag-NORs in A. ephippium were observed in the terminal regions of the short arms of an acrocentric pair as well as those in the other species already studied. C-banding pattern showed species-specific features and the Ag- NORs were C-band positive in both species. On the basis of the molecular phylogeny and the chromosomal location of NORs, it is inferred that the terminal type of NOR-location is original in anemonefish evolution and the interstitial type of NOR-location in A. ocellaris has been changed from the terminal type by the occurrence of pericentric inversion including NORs. [ABSTRACT FROM AUTHOR]

Nucleolar dominance (ND) is an epigenetic, developmentally regulated phenomenon that describes the selective inactivation of 35S rDNA loci derived from one progenitor of a hybrid or allopolyploid. The presence of ND was documented in an allotetraploid grass, Brachypodium hybridum (genome composition DDSS), which is a polyphyletic species that arose from crosses between two putative ancestors that resembled the modern B. distachyon (DD) and B. stacei (SS). In this work, we investigated the developmental stability of ND in B. hybridum genotype 3-7-2 and compared it with the reference genotype ABR113. We addressed the question of whether the ND is established in generative tissues such as pollen mother cells (PMC). We examined condensation of rDNA chromatin by fluorescence in situ hybridization employing state-of-art confocal microscopy. The transcription of rDNA homeologs was determined by reverse-transcription cleaved amplified polymorphic sequence analysis. In ABR113, the ND was stable in all tissues analyzed (primary and adventitious root, leaf, and spikes). In contrast, the 3-7-2 individuals showed a strong upregulation of the S-genome units in adventitious roots but not in other tissues. Microscopic analysis of the 3-7-2 PMCs revealed extensive decondensation of the D-genome loci and their association with the nucleolus in meiosis. As opposed, the S-genome loci were always highly condensed and localized outside the nucleolus. These results indicate that genotype-specific loss of ND in B. hybridum occurs probably after fertilization during developmental processes. This finding supports our view that B. hybridum is an attractive model to study ND in grasses. [ABSTRACT FROM AUTHOR]

The ubiquitous presence of rRNA genes in nuclear, plastid, and mitochondrial genomes has provided an opportunity to use genomic markers to infer patterns of molecular and organismic evolution as well as to assess systematic issues throughout the tree of life. The number, size, location, and activity of the 35S rDNA cistrons in plant karyotypes have been used as conventional cytogenetic landmarks. Their scrutiny has been useful to infer patterns of chromosomal evolution and the data have been used as a proxy for assessing species discrimination, population differentiation and evolutionary relationships. The correct interpretation of rDNA markers in plant taxonomy and evolution is not free of drawbacks given the complexities derived from the lability of the genetic architecture, the diverse patterns of molecular change, and the fate and evolutionary dynamics of the rDNA units in hybrids and polyploid species. In addition, the terminology used by independent authors is somewhat vague, which often complicates comparisons. To date, no efforts have been reported addressing the potential problems and limitations involved in generating, utilizing, and interpreting the data from the 35S rDNA in cytogenetics. This review discusses the main technical and conceptual limitations of these rDNA markers obtained by cytological and karyological experimental work, in order to clarify biological and evolutionary inferences postulated in a systematic and phylogenetic context. Also, we provide clarification for some ambiguity and misconceptions in terminology usually found in published work that may help to improve the usage of the 35S ribosomal world in plant evolution. [ABSTRACT FROM AUTHOR]

Nucleolar dominance (ND) is an epigenetic, developmentally regulated phenomenon that describes the selective inactivation of 35S rDNA loci derived from one progenitor of a hybrid or allopolyploid. The presence of ND was documented in an allotetraploid grass, Brachypodium hybridum (genome composition DDSS), which is a polyphyletic species that arose from crosses between two putative ancestors that resembled the modern B. distachyon (DD) and B. stacei (SS). In this work, we investigated the developmental stability of ND in B. hybridum genotype 3-7-2 and compared it with the reference genotype ABR113. We addressed the question of whether the ND is established in generative tissues such as pollen mother cells (PMC). We examined condensation of rDNA chromatin by fluorescence in situ hybridization employing state-of-art confocal microscopy. The transcription of rDNA homeologs was determined by reverse-transcription cleaved amplified polymorphic sequence analysis. In ABR113, the ND was stable in all tissues analyzed (primary and adventitious root, leaf, and spikes). In contrast, the 3-7-2 individuals showed a strong upregulation of the S-genome units in adventitious roots but not in other tissues. Microscopic analysis of the 3-7-2 PMCs revealed extensive decondensation of the D-genome loci and their association with the nucleolus in meiosis. As opposed, the S-genome loci were always highly condensed and localized outside the nucleolus. These results indicate that genotype-specific loss of ND in B. hybridum occurs probably after fertilization during developmental processes. This finding supports our view that B. hybridum is an attractive model to study ND in grasses. [ABSTRACT FROM AUTHOR]

The ubiquitous presence of rRNA genes in nuclear, plastid, and mitochondrial genomes has provided an opportunity to use genomic markers to infer patterns of molecular and organismic evolution as well as to assess systematic issues throughout the tree of life. The number, size, location, and activity of the 35S rDNA cistrons in plant karyotypes have been used as conventional cytogenetic landmarks. Their scrutiny has been useful to infer patterns of chromosomal evolution and the data have been used as a proxy for assessing species discrimination, population differentiation and evolutionary relationships. The correct interpretation of rDNA markers in plant taxonomy and evolution is not free of drawbacks given the complexities derived from the lability of the genetic architecture, the diverse patterns of molecular change, and the fate and evolutionary dynamics of the rDNA units in hybrids and polyploid species. In addition, the terminology used by independent authors is somewhat vague, which often complicates comparisons. To date, no efforts have been reported addressing the potential problems and limitations involved in generating, utilizing, and interpreting the data from the 35S rDNA in cytogenetics. This review discusses the main technical and conceptual limitations of these rDNA markers obtained by cytological and karyological experimental work, in order to clarify biological and evolutionary inferences postulated in a systematic and phylogenetic context. Also, we provide clarification for some ambiguity and misconceptions in terminology usually found in published work that may help to improve the usage of the 35S ribosomal world in plant evolution.

Nucleolar dominance (ND) is an epigenetic, developmentally regulated phenomenon that describes the selective inactivation of 35S rDNA loci derived from one progenitor of a hybrid or allopolyploid. The presence of ND was documented in an allotetraploid grass, Brachypodium hybridum (genome composition DDSS), which is a polyphyletic species that arose from crosses between two putative ancestors that resembled the modern B. distachyon (DD) and B. stacei (SS). In this work, we investigated the developmental stability of ND in B. hybridum genotype 3-7-2 and compared it with the reference genotype ABR113. We addressed the question of whether the ND is established in generative tissues such as pollen mother cells (PMC). We examined condensation of rDNA chromatin by fluorescence in situ hybridization employing state-of-art confocal microscopy. The transcription of rDNA homeologs was determined by reverse-transcription cleaved amplified polymorphic sequence analysis. In ABR113, the ND was stable in all tissues analyzed (primary and adventitious root, leaf, and spikes). In contrast, the 3-7-2 individuals showed a strong upregulation of the S-genome units in adventitious roots but not in other tissues. Microscopic analysis of the 3-7-2 PMCs revealed extensive decondensation of the D-genome loci and their association with the nucleolus in meiosis. As opposed, the S-genome loci were always highly condensed and localized outside the nucleolus. These results indicate that genotype-specific loss of ND in B. hybridum occurs probably after fertilization during developmental processes. This finding supports our view that B. hybridum is an attractive model to study ND in grasses.

Karyotypes in 12 taxa of Gundelia are compared, based on Feulgen-stained somatic metaphase chromosomes. The karyotypes of G. anatolica, G. asperrima, G. cilicica, G. colemerikensis, G. dersim, G. glabra, G. komagenensis, G. mesopotamica, G. munzuriensis and G. vitekii are described for the first time. Karyological analyses indicate relationships among the species with respect to their asymmetry indices. All Gundelia species studied were diploid with 2n = 2x = 18 chromosomes. All karyotypes are symmetrical, consisting of metacentric and submetacentric chromosomes. The submetacentric chromosomes of all the investigated specimens contain a secondary constriction. Three chromosome types were identified according to the position of the secondary constrictions. The chromosomes ranged in size from 2.00 µm to 7.02 µm. The total haploid chromosome length (THL) varied from 24.97 μm (G. asperrima) to 42.56 μm (G. rosea). To determine the karyological relationships among taxa, PCoA (Principal Coordinate Analysis) with six uncorrelated parameters was performed.

Karyotypes in 16 representative taxa of the Ophrys genus are compared, based on Feulgen-stained somatic metaphase chromosomes. The karyotypes of O. omegaifera subsp. israelitica, O. ulupinara, O. lycia, O. argolica subsp. lucis, O. argolica subsp. lesbis, O. climacis and O. reinholdii subsp. reinholdii are described for the first time. Karyological analyses indicate relationships among the species with respect to their asymmetry indices. All Ophrys taxa studied were diploid with 2n = 2x = 36 chromosomes. One B chromosome has been detected among the chromosomes of O. argolica subsp. lucis. All karyotypes are symmetrical, consisting of metacentric and submetacentric chromosomes. The longest chromosomes of all the investigated specimens contain a secondary constriction. It is determined that there is a correlation between the total number of chromosomes having secondary constrictions and the evolutionary development order of the taxa. Based on nuclear DNA content, analysis was carried out by flow cytometer using propodium iodide as fluorochrome, 2C nuclear DNA content of 16 Ophrys species varying between 20.80 pg (O. argolica subsp. lucis) and 23.11 pg (O. omegaifera subsp. israelitica). Karyotype asymmetry relationships are discussed according to the bidimensional scatter plots of A1-A2, CVCL- CVCI, CVCL-MCA and CVCI-MCA. [ABSTRACT FROM AUTHOR]

Nephilid systematics has been subject to several changes in the last years, and the use of non-classical characters could be useful for evolutionary considerations. In this study, we analyzed the mitotic chromosomes of two nephilid spiders,Nephila clavipesandNephila sexpunctata, using standard staining, silver nitrate impregnation and C-banding techniques, aiming to discuss the chromosomal similarities of Nephilidae and Tetragnathidae, and chromosome evolution withinNephilaandNephilingis. The basic karyotype characteristics observed in these two species (2n♂ = 22 + X1X20 and monoarmed chromosomes) were similar to those registered for most araneoid families, i.e., Araneidae, Linyphiidae, Nephilidae, Nesticidae and Tetragnathidae. However, the occurrence of both prominent secondary constrictions and nucleolar organizer regions (NORs) is a shared characteristic between Nephilidae and Tetragnathidae, considering that these regions were not observed in any other Araneoidea species cytogenetically examined. Furthermore, in the present study we showed that withinNephilaandNephilingisspecies, change in the number and location of NORs as well as in the quantity and distribution of constitutive heterochromatin were the main events responsible for chromosome evolution, and that these differences can be useful in the cytotaxonomy of this group. [ABSTRACT FROM AUTHOR]

New morphological data on chromosome complement of diplozoid parasite Paradiplozoon megan from the chub Squalius cephalus are shown herein. The karyotype of P. megan is characterized by seven pairs (2 n = 14) of medium long (up to 11 μm) one-armed chromosomes which are nearly identical in number and morphological classification with chromosomes of other Paradiplozoon species described karyologically to date ( Paradiplozoon bliccae, Paradiplozoon nagibinae, Paradiplozoon sapae, Paradiplozoon pavlovskii and Paradiplozoon homoion). A single locus for ribosomal RNA genes, visualized in the secondary constriction site by the fluorescent in situ hybridization method, is situated interstitially on a median part of a long arm of the smallest, 7th chromosome pair in P. megan. Phylogenetic interrelationships within the members of the family Diplozoidae and hypothesis for the ancestral karyotype are discussed here. [ABSTRACT FROM AUTHOR]

Garcinia indica (Cluasiaceae) is a tree species endemic to Western Ghats of Maharashtra. Fruits are important as they are the rich source of hydroxy citric acid. Being polygamodioecious, plants in different locations show a lot of variation in height of plant, branching pattern, canopy, leaf and fruit morphology. Hence a cytological study was undertaken to see whether the polymorphism also exists at genetic level. Roots from germinating seeds were pre-treated with saturated p-dichlorobenzene. Squash was made by propionic acid orcein method. Chromosome number reported was 2n=54. The karyotype of G. indica consists of 7 pairs of metacentric chromosomes, 17 pairs of submetacentric chromosomes, 1 pair of submetacentric chromosomes with satellites, 1 pair of submetacentric chromosomes with secondary constriction and one asymmetric pair of chromosomes. [ABSTRACT FROM AUTHOR]

The detailed karyotypes of diploid (2n = 2x = 24) and triploid (2n = 3x = 36) of L. tigrinum were constructed based on fluorescence in situ hybridization (FISH) using 5S rDNA and 45S rDNA probes. The lengths of mitotic metaphase chromosomes ranged from 15.92 to 30.18 um, with a total length/genome of 250.46 um in diploid, and 15.24 to 28.16 um, with a total length/genome of 233.42 um in triploid. The chromosome composed of two pairs of metacentrics (Chromosomes 1 and 2), four pairs of subtelocentrics (Chromosomes 3, 4, 5, and 6) and six pairs of telocentrics (Chromosomes 7, 8, 9, 10, 11, and 12) in diploid L. tigrinum, two pairs of metacentrics (Chromosomes 1 and 2), six pairs of subtelocentrics (Chromosomes 3, 4, 5, 6, 7, and 11) and four pairs of telocentrics (Chromosomes 8, 9, 10, and 12) in triploid L. tigrinum. Ten (Chromosomes 1, 2, 6, 7, and 11) or twelve (Chromosomes 1, 2, 4, 6, 7, and 11) loci of 45S rDNA were detected in the diploid chromosomes whereas fifteen loci were detected in triploid chromosomes (Chromosomes 1, 2, 6, 7, and 11). Two loci of 5S rDNAs were located close to each other at the both diploid and triploid chromosome 3. New cytotypes of secondary constriction were observed in diploid (1-1-1-0) and triploid (3-2-1-1). [ABSTRACT FROM AUTHOR]