Telocentric Chromosomes Research Articles

A working model for the formation of Robertsonian chromosomes.

Robertsonian chromosomes form by fusion of two chromosomes that have centromeres located near their ends, known as acrocentric or telocentric chromosomes. This fusion creates a new metacentric chromosome and is a major mechanism of karyotype evolution and speciation. Robertsonian chromosomes are common in nature and were first described in grasshoppers by the zoologist W. R. B. Robertson more than 100 years ago. They have since been observed in many species, including catfish, sheep, butterflies, bats, bovids, rodents and humans, and are the most common chromosomal change in mammals. Robertsonian translocations are particularly rampant in the house mouse, Mus musculus domesticus, where they exhibit meiotic drive and create reproductive isolation. Recent progress has been made in understanding how Robertsonian chromosomes form in the human genome, highlighting some of the fundamental principles of how and why these types of fusion events occur so frequently. Consequences of these fusions include infertility and Down's syndrome. In this Hypothesis, I postulate that the conditions that allow these fusions to form are threefold: (1) sequence homology on non-homologous chromosomes, often in the form of repetitive DNA; (2) recombination initiation during meiosis; and (3) physical proximity of the homologous sequences in three-dimensional space. This Hypothesis highlights the latest progress in understanding human Robertsonian translocations within the context of the broader literature on Robertsonian chromosomes.

First cytogenetic study of the Somphong’s rasbora (Trigonostigma somphongsi) (Perciformes, Cyprinidae), a critically endangered species in Thailand

The first chromosome study of Trigonostigma somphongsi (Meinken,1958) from Thailand. Specimens were collected from Pak Phli District, Nakhornnayok Province, central Thailand. The mitotic chromosomes were directly prepared from kidney tissues of two males and two females. Conventional staining and Ag-NOR banding techniques were applied to stain the chromosomes. The results shown that diploid chromosome number of T. somphongsi was 2n=50, the fundamental numbers (NF) were 92 in both male and female. The types chromosomes consisted of 10 metacentric, 20 submetacentric, 12 acrocentric and 8 telocentric chromosomes. The result also exhibited that the interstitial nucleolar organizer regions (NORs) were clearly observed at the short arm of chromosome pair 2. The karyotype formula could be deduced as: 2n (diploid) 50=10m+20sm+12a+8t.

Chromosome ends initiate homologous chromosome pairing during rice meiosis.

During meiotic prophase I, chromosomes undergo large-scale dynamics to allow homologous chromosome pairing, prior to which chromosome ends attach to the inner nuclear envelope and form a chromosomal bouquet. Chromosome pairing is crucial for homologous recombination and accurate chromosome segregation during meiosis. However, the specific mechanism by which homologous chromosomes recognize each other is poorly understood. Here, we investigated the process of homologous chromosome pairing during early prophase I of meiosis in rice (Oryza sativa) using pooled oligo probes specific to an entire chromosome or chromosome arm. We revealed that chromosome pairing begins from both ends and extends toward the center from early zygotene through late zygotene. Genetic analysis of both trisomy and autotetraploidy also showed that pairing initiation is induced by both ends of a chromosome. However, healed ends that lack the original terminal regions on telocentric and acrocentric chromosomes cannot initiate homologous chromosome pairing, even though they may still enter the telomere clustering region at the bouquet stage. Furthermore, a chromosome that lacks the distal parts on both sides loses the ability to pair with other intact chromosomes. Thus, the native ends of chromosomes play a crucial role in initiating homologous chromosome pairing during meiosis and likely have a substantial impact on genome differentiation.

Taxonomic notes, distribution update and the first chromosomal analysis of Vectius niger (Simon, 1880) and Trochanteria gomezi Canals, 1933 (Araneae: Trochanteriidae).

Spiders of the family Trochanteriidae are characterized by the carapace being extremely flat, with a reflex border, medium posterior eyes flattened, laterigrade legs, the absence of claw tufts, anterior lateral spinnerets with an incomplete distal article, and an inflatable and epiginal plate formed by a divided plate. Two out of the six worldwide genera of Trocantheriids have species in the Brazilian areas: Trochanteria Karsch and Vectius Simon. Here we present the redescription of Vectius niger and morphological data of Trochanteria gomezi, with an expansion of the distribution of these species in the Neotropical region and unpublished chromosomal data of both species. Mitotic and meiotic cells of both T. gomezi and V. niger showed 2n=22 and 2n=24 telocentric chromosomes, with a sex chromosome system of the type X1X2 in males/X1X1X2X2 in females. The chromosomal data shown here matches those found in trochanteriids to date.

Chromosome Diversity and Evolution of the Endemic Malagasy Velvet Geckos of the Genus Blaesodactylus (Reptilia, Gekkonidae).

We performed a molecular and phylogenetic analysis and a comparative cytogenetic study with standard karyotyping, silver staining (Ag-NOR) and sequential C-banding + Giemsa, + fluorochromes on several Blaesodactylus samples. The phylogenetic inference retrieved two main clades, the first comprises B. victori, B. microtuberculatus and B. boivini, while the second includes B. sakalava, B. antongilensis and B. ambonihazo. The available samples of B. sakalava form two different clades (here named B. sakalava clade A and clade B), which probably deserve a taxonomic re-evaluation. We found a karyological variability in Blaesodactylus in terms of chromosome number (2n = 40-42), morphology, location of NORs, and heterochromatin distribution pattern. Blaesodactylus antongilensis and B. sakalava clade A and B showed a karyotype of 2n = 40 mostly telocentric chromosomes. Pairs 1 and 6 were metacentric in B. sakalava clade A and B, while pair 1 was composed of subtelocentric/submetacentric elements in B. antongilensis. In contrast, B. boivini displayed a karyotype with 2n = 42 only telocentric chromosomes. NORs were on the first chromosome pair in B. boivini, and on the second pair in B. antongilensis. Adding our data to those available from the literature on evolutionarily related species, we highlight that the chromosome diversification in the genus probably proceeded towards a progressive reduction in the chromosome number and the formation of metacentric elements.

First report of chromosome and karyological analysis of Gekko nutaphandi (Gekkonidae, Squamata) from Thailand: Neo-diploid chromosome number in genus Gekko

The karyotypes of red-eyed Gecko are not reported yet. Herein, we describe the karyotypes of red-eyed Gecko (Gekko nutaphandi Bauer, Sumontha & Pauwels, 2008) from Thailand. Gecko chromosome preparations were directly conducted from bone marrow and testis. Chromosomal characteristics were analyzed by Giemsa staining, Ag-NOR banding as well as fluorescence in situ hybridization (FISH) using microsatellites d(GC)15 probe. The results showed that the number of diploid chromosomes is 2n=34, while the fundamental number (NF) is 46 in both males and females. The types of chromosomes were 4 large metacentric, 6 large submetacentric, 2 medium telocentric, 2 small metacentric and 20 small telocentric chromosomes. The results of conventional Giemsa staining presented the diploid chromosome number differentiation even in the same genus. NORs are located at the secondary constriction to the telomere on the long arm of chromosome pair 5. There are no sex differences in karyotypes between males and females. FISH with d(GC)15 sequences were also displayed at the telomeres of most other chromosomes. We found that during metaphase I the homologous chromosomes showed synapsis, which can be defined as 19 ring bivalents and 17 haploid chromosomes (n=17) at metaphase II as a diploid species. The karyotype formula is as follows: 2n (34) = L4m+L6sm+M2t+S2m+S20t.

Karasu ırmağında (Erzurum) yayılış gösteren Chondrostoma regium'un (Teleostei: Leuciscidae) karyotipik analizleri

In this study, the karyotypic characteristics of Chondrostoma regium (Heckel, 1843) have been investigated. Fish samples were caught from the Karasu River (Euphrates River Basin) with fishing net. The live fish were transported to the laboratory and kept in aerated aquaria before the analyses. The karyotype analysis was performed in fish kidney and gill epithelium cells. It was determined that C. regium had 2n=50 chromosomes. In detail, the karyotype formula of C. regium was determined as 9 metacentric, 7 submetacentric, 1 subtelocentric and 8 telocentric chromosome pairs (18M+14SM+2ST+16T), and fundamental arm number was calculated as 82. Constitutive heterochromatin regions were determined on telomeres of the chromosomes. Nuclear orgnizer regions were detected on 21st chromosome. Karyotype symmetry/asymmetry index was calculated as 2.32. The karyotypes of gill and kidney cells were the same. No sex chromosomes were cytologically detected.

Chromosome Mapping of Repetitive DNAs in the Picasso Triggerfish (Rhinecanthus aculeatus (Linnaeus, 1758)) in Family Balistidae by Classical and Molecular Cytogenetic Techniques

This work presents the cytogenetic analysis conducted on the Picasso triggerfish (Rhinecanthus aculeatus (Linnaeus, 1758)) from Thailand. Mitotic chromosomes were prepared from the anterior kidney. The cell suspensions were harvested by in vivo colchicine treatment. The present study includes the chromosomal investigation on R. aculeatus, using conventional (Giemsa staining, Ag-NOR and C-banding) and molecular approaches (in situ mapping of five different repetitive DNA classes including 18S rDNA, 5S rDNA, (CA)15, (GA)15 and (CAA)10 as markers.) The results showed that R. aculeatus has karyotypes formed exclusively by telocentric chromosomes (44t; NF=44). The C-positive heterochromatic blocks are preferentially located in the centromeric and telomeric regions of some chromosomal pairs. The Ag-NOR sites occupy the interstitial position of the long arms of the largest telocentric pair (pair 1). The exclusive location of the major ribosomal sites in these pairs was confirmed by hybridization with 18S rDNA probes. However, the 5S rDNA genes are not located on 18S rDNA-bearing chromosomes, but instead located exclusively in the subcentromeric region of pair 4. The mapping of (CA)15, (GA)15 and (CAA)10 microsatellites are sparsely dispersed along all the chromosomes. The karyotype formula of R. aculeatus is 2n (44) = 44t.

Chromosome Complement of Pomatoschistus marmoratus and Karyotype Evolution in Sand Gobies (Gobiidae: Gobionellinae)

The family Gobiidae constitutes one of the most diverse groups among teleost fish; some of its species are objects of aquaculture and fisheries. Despite many years of cytogenetic studies, the chromosome complements of many species of gobies remain unknown, and the trends of karyotypic evolution are poorly understood. Here I describe a previously unstudied karyotype of a widespread species from the group of sand gobies (Pomatoschistus marmoratus) and analyze the trends of karyotypic evolution of this group in comparison with other taxonomic groups of gobies from the Atlantic-Mediterranean and Ponto-Caspian regions. For P. marmoratus, the diploid number is 2n=46; it consists of 11 pairs of submetacentric chromosomes, 12 pairs of subtelocentric and telocentric chromosomes (NF=68). A comparative karyological analysis showed that the main trend in the karyotypic evolution of sand gobies differs from that of other groups of gobies and is associated with an increase in the number of chromosomal arms as a result of chromosomal rearrangements leading to a change in the centromere position. The results obtained contribute to understanding the role of chromosomal rearrangements in the evolution of Gobiidae and are of interest for further cytogenetic studies of this large family of fish.

Chromosomal Study on Selected Small Araneomorph Spiders from Brazil, Including the First Records in Palpimanidae and Theridiosomatidae (Araneae, Araneomorphae).

Among the 50,474 spider species, only 849 have chromosomal data available in the literature. Fifty spider families remain unknown from a cytogenetic perspective. The aim of this study was to analyze chromosomally selected araneomorph spiders from Brazil, to contribute to the cytotaxonomy and chromosome evolution of this group. The karyotypes of 12 species belonging to families Corinnidae, Linyphiidae, Oonopidae, Palpimanidae, Theridiidae, Theridiosomatidae, Trachelidae, and Zodariidae were analyzed, including the first chromosomal record for the first two families. Specimens (with the abdomen content partially exposed by perforation) were subjected to colchicine, hypotonization, and fixation. In most cases, the total content of the abdomen was used to prepare slides by spreading of cell suspension and subsequent Giemsa staining. The results were as follows: Cinetomorpha simplex Simon, 1892 (Oonopidae) 2n♂ = 9, X0; Neotrops sp. and Neoxyphinus termitophilus (Oonopidae), 2n♂ = 7, X0; Otiothops birabeni (Palpimanidae); Agyneta sp. (Linyphiidae), 2n♂ = 24, X1X20; Coleosoma floridanum, Thymoites sp.1 and Thymoites sp.2 (Theridiidae), 2n♂ = 22, X1X20; Naatlo sp. (Theridiosomatidae), 2n♂ = 30, X1X20; Orthobula sp. (Trachelidae) 2n♂ = 21, X0; Falconina sp. (Corinnidae), 2n♂ = 28, X1X20; Epicratinus sp. (Zodariidae) 2n♂ = 42, X1X20. The chromosomal morphology was determined for all the samples except for Oonopidae. Most species exhibited telocentric chromosomes, with the exception of Palpimanidae and Theridiosomatidae. The main findings: 1) support an hypothesis on ancestral karyotype of Zodariidae and Oonopidae; 2) reveal a relatively high chromosome number in Palpimanidae that supports an idea on relatively high ancestral chromosome number (2n♂ = 42) of entelegyne spiders (Palpimanoidea is sister group of entelegyne spiders); 3) show that the karyotype found in Theridiosomatidae is exceptional within the Araneoidea.

Tracking Chromosomal Origins in the Northern Italy System of Metacentric Races of the House Mouse

The Western European house mouse is chromosomally diverse, with diploid karyotypes ranging from the standard 40 telocentric chromosomes down to 22 chromosomes. Karyotypes are modified through Robertsonian (Rb) fusion of 2 telocentrics into a single metacentric, occurring repeatedly with fixation, and whole-arm reciprocal translocations (WARTs) generating additional novel karyotypes. Over 100 metacentric populations (chromosomal races) have been identified, geographically clustered into “systems.” Chromosomal races within systems often hybridise, and new races may emerge through this hybridisation (“zonal raciation”). We wished to determine the degree to which chromosomal races in a system have evolved independently or share common ancestry. Recombination between chromosomes from hybridising chromosomal races can erase the signals associated with a particular metacentric of interest, making inferences challenging. However, reduced recombination near the centromeres of chromosomal race-specific metacentrics makes centromere-adjacent markers ideal for solving this problem. For the Northern Italy System (NIS), we used microsatellite markers near the centromere to test previous hypotheses about evolutionary relationships of 5 chromosomal races. We chose markers from chromosomes 1, 3, 4, and 6, all of which comprise one arm of a metacentric in at least 2 of these NIS metacentric populations. We used estimates of F_ST and R_ST, as well as principal components analyses and neighbour-joining phylogenetic analyses, to infer evolutionary relationships between these 5 chromosomal races and neighbouring mice with the standard karyotype. We showed that the metacentric populations form a single grouping distinct from the standard populations, consistent with their common origin and consistent with a parsimonious sequence of chromosomal rearrangements to explain the relationship of the chromosomal races. That origin and evolution of the chromosomal races in the system would have involved Rb fusions, explaining the occurrence of chromosomal races with diploid numbers as low as 22. However, WARTs and zonal raciation have also been inferred, and the rare occurrence of chromosome 1 in different metacentrics in closely related chromosomal races is almost certainly explained by a WART. Our results with centromeric microsatellites are consistent with the above scenarios, illustrating, once again, the value of markers in the centromeric region to test evolutionary hypotheses in house mouse chromosomal systems.

Quantitative analysis of Robertsonian chromosomes inherited by descendants from multiple Rb heterozygotes of Mus m. Domesticus.

Robertsonian translocation is the most common chromosomal rearrangement in mammals, and represents the type of chromosomal change that most effectively contributes to speciation in natural populations. Rb translocations involve double-strand DNA breaks at the centromere level in two telocentric chromosomes, followed by repair ligation of the respective long arms, creating a metacentric Rb chromosome. Many different chromosomal races have been described in Mus musculus domesticus that show reduced chromosome numbers due to the presence of Rb metacentric chromosomes. The crossroads between ancestral telocentrics and the new metacentric chromosomes should be resolved in the meiotic cells of the heterozygote individuals, which form trivalents. The preferential segregation of metacentric chromosomes to the egg during female meiosis I has been proposed to favor their fixation and eventual conversion of a telocentric karyotype to a metacentric karyotype. This biased segregation, a form of meiotic drive, explains the karyotype changes in mammalian species that have accumulated Rb fusions. We studied and compared the number of Rb chromosomes inherited by the offspring of multiple Rb heterozygous of M. domesticus in reciprocal crosses. We did not find that the Rb chromosomes were inherited preferentially with respect to the telocentric chromosomes; therefore, we found no evidence for the meiotic drive, nor was there a random distribution of Rb chromosomes inherited by the descendants.

Mega-sized pericentromeric blocks of simple telomeric repeats and their variants reveal patterns of chromosome evolution in ancient Cycadales genomes.

Simple telomeric repeats composed of six to seven iterating nucleotide units are important sequences typically found at the ends of chromosomes. Here we analyzed their abundance and homogeneity in 42 gymnosperm (29 newly sequenced), 29 angiosperm (one newly sequenced), and eight bryophytes using bioinformatics, conventional cytogenetic and molecular biology approaches to explore their diversity across land plants. We found more than 10 000-fold variation in the amounts of telomeric repeats among the investigated taxa. Repeat abundance was positively correlated with increasing intragenomic sequence heterogeneity and occurrence at non-telomeric positions, but there was no correlation with genome size. The highest abundance/heterogeneity was found in the gymnosperm genus Cycas (Cycadaceae), in which megabase-sized blocks of telomeric repeats (i.e., billions of copies) were identified. Fluorescent in situ hybridization experiments using variant-specific probes revealed canonical Arabidopsis-type telomeric TTTAGGG repeats at chromosome ends, while pericentromeric blocks comprised at least four major telomeric variants with decreasing abundance: TTTAGGG>TTCAGGG >TTTAAGG>TTCAAGG. Such a diversity of repeats was not found in the sister cycad family Zamiaceae or in any other species analyzed. Using immunocytochemistry, we showed that the pericentromeric blocks of telomeric repeats overlapped with histone H3 serine 10 phosphorylation signals. We show that species of Cycas have amplified their telomeric repeats in centromeric and telomeric positions on telocentric chromosomes to extraordinary high levels. The ancestral chromosome number reconstruction suggests their occurrence is unlikely to be the product of ancient Robertsonian chromosome fusions. We speculate as to how the observed chromosome dynamics may be associated with the diversification of cycads.

First Report on Classical and Molecular Cytogenetics of Doi Inthanon Bent-toed Gecko, Cyrtodactylus inthanon Kunya et al., 2015 (Squamata: Gekkonidae) in Thailand

This study analyzed the karyotype of Cyrtodactylus inthanon Kunya et al., 2015 from Doi Inthanon, Chiang Mai Province, northern Thailand. The metaphase and meiotic chromosome preparations were obtained by squash technique from bone marrow and testes, respectively. The chromosomes were stained by Giemsa staining, Ag-NOR banding and molecular cytogenetics with ?uorescence in situ hybridization (FISH) using microsatellites d(CA)15, d(GC)15, d(CAG)10 and d(GAA)10 as probes. The results showed the diploid chromosome number (2n) of 40. The chromosome types of metacentric, submetacentric, acrocentric and telocentric chromosomes were 12-4-2-22, respectively. The Ag-NORs banding technique provides the pair of nucleolar organizer regions (NORs) on the telomeric region of the long arm of acrocentric pair 12. There are no sex differences in karyotypes between males and females. We also found that during metaphase I on meiosis of C. inthanon, the homologous chromosomes appeared synapsis of 20 bivalents. The microsatellite d(CA)15 signals were located on the sub-centromeric region of the metacentric pair 10, whereas the d(GC)15, d(CAG)10 and d(GAA)10 repeats are highly accumulated throughout almost all entire chromosomes. The karyotype formula is as follows: C. inthanon (2n = 40), Lm2 + Lsm4 + Lt6 + Mm2 + Mt8 + Sm8 + Sa2 + St8.

Classical chromosome features and microsatellites repeat in Gekko petricolus (Reptilia, Gekkonidae) from Thailand

The objectives of this study were to examine size, shape, diploid number (2n), fundamental number (NF), NORs region, and distribution of microsatellite by using Fluorescence in situ hybridization technique (FISH) and to establish the karyotype and standard idiogram of sandstone geckos (Gekko petricolus Taylor, 1962). Sandstone gecko distributed in the sandstone mountains in Laos, Cambodia, and Thailand. Five male and five female specimens were collected from Ubon Ratchathani and Mukdahan provinces, Thailand. The metaphase cells were directly prepared from the bone marrow cells. Chromosomes were stained by conventional staining, NORs-banding and FISH techniques. The results found that the diploid number was 38 chromosomes. The fundamental number was 54. The karyotype composed of 4 large metacentric, 4 large acrocentric, 2 large telocentric, 4 medium acrocentric, 2 medium telocentric, 2 small submetacentric, 2 small acrocentric and 18 small telocentric chromosomes. No morphological difference was identified between sex chromosomes of male and female specimens. The NORs appeared to telomere of the long arm of chromosome pair 17. The study displayed that the distribution of microsatellite using (CA)15 and (GAA)10 probes distributed throughout the genome. However, (CA)15 sequences concentrated in the telomere. The karyotype formula G. petricolus is as follow: 2n (38) = Lm4+La4+Lt2+Ma4+Mt2+Ssm2+Sa2+St18.

Chromosomal description of three Dixonius (Squamata, Gekkonidae) from Thailand

Chromosomal characteristics and karyological analysis of three Dixonius, including D. hangseesom, D. siamensis and D. melanostictus, from Thailand were studied. Chromosome preparations were conducted by squash technique from bone marrow and testis. Conventional Giemsa’s staining and Ag-NOR banding techniques were applied to stain the chromosome. The results showed that the diploid chromosomes are 2n=40, for D. hangseesom and D. siamensis; and 2n=42, for D. melanostictus. The fundamental number (NF) is 42 in D. hangseesom and D. siamensis and 44 in D. melanostictus. The types of chromosomes were 2 metacentrics and 38 telocentrics for D. hangseesom and D. siamensis, while the karyotype of D. melanostictus comprised 2 acrocentrics and 40 telocentrics. In the D. hangseesom and D. siamensis, NORs are located to the near centromere on long arm of the telocentric chromosome pair 13. Although, the NORs of D. melanostictus are situated on the subtelomeric region of telocentric chromosome pair 8. There are no sex differences in karyotypes between males and females of these three geckos species. We found that during metaphase I and metaphase II on male meiosis of the D. hangseesom and D. siamensis, the homologous chromosomes showed synapsis of 20 bivalents and 20 haploid chromosomes (n=20). Moreover, metaphase I and metaphase II of the male D. melanostictus showed synapsis of 21 bivalents and 21 haploid chromosomes (n=21). Their karyotype formulas is as follows: D. hangseesom (2n=40): Lm2 + Lt2 + Mt4 + St32, D. siamensis (2n=40): Lm2 + Lt6 + Mt4 + St28, and D. melanostictus (2n=42): La2 + Lt12 + Mt4 + St24.

First karyotype description of the species of Adenomera Steindachner, 1867 (Anura, Leptodactylidae) in the " thomei" clade.

The genus Adenomera Steindachner, 1867 currently comprises 29 nominal species, some of which are suggested to be cryptic species complexes. The present study was carried out with specimens of the "thomei" clade that encompasses three taxa distributed in the Atlantic Forest biome: Adenomerathomei Almeida et Angulo, 2006, Adenomera sp. L., and Adenomera sp. M. We used classical cytogenetics to describe the diploid number and karyomorphology of these three species collected in two different locations in the state of Bahia, Brazil. Our results revealed the diploid number 2n = 24 (FN = 34) with two pairs of metacentric chromosomes (pairs 1 and 5), three pairs of submetacentric chromosomes (pairs 2, 3, and 4), and seven pairs of telocentric chromosomes (pairs 6, 7, 8, 9, 10, 11, and 12). Further morphological, bioacoustic, and cytogenetic data (C-banding and AgNor) are needed to better delineate the lineages within the "thomei" clade.

Comparative cytological studies of naturally grown plants and in vitro grown plants of Gynura procumbens – an important medicinal plant species

Summary Introduction: Gynura procumbens is an important medicinal plant that contains different types of chemical constituents that show tremendous curative effects. Objective: The aim of this research work was comparative karyomorphological analysis between in vitro and in vivo grown selected medicinal plant species. Methods: The roots were collected properly from naturally grown plants and in vitro propagated plants and pretreated with 1,4-para-dichlorobenzene (PDB) for 2.00 – 3.00 hours at room temperature. After pretreating with PDB the roots were washed thoroughly and kept in 1:3 (v/v) aceto-alcohol for 24 hours and then, transferred to 70% alcohol (v/v) for preservation. After that completing staining process, prepared slides were observed under microscope for karyotype analysis & ideogram preparation. Results: This research work reveled that both mother plant and tissue culture raised plants had 2n=20 chromosomes in somatic cell. No telocentric or acrocentric chromosome observed in the basic set of chromosomes. Both plants had 3 submetacentric and 7 metacentric chromosomes in the basic set of chromosomes. The centromeric formula for both plants was 3sm + 7m. The length of individual chromosome of in vivo plants ranged from 6.20 to 11.24 µm, whereas chromosome length of in vitro grown plants ranged from 6.08 to 11.22 µm. The total form percent (TF%) of naturally grown plants and micro-propagated plants were same (43.93%). Mother plant had 2A type of karyotype, the formula being 2Lsm + 4Msm + 4Mm + 10Sm. In vitro grown plant had also 2A type of karyotype which could be expressed by the formula, 2Lsm + 4Msm + 2Mm + 12Sm. Conclusion: The results of cytological studies point out that chromosome numbers of naturally grown plants and micro-propagated plants were same. There were very little karyotypic variations observed in case of both micropropagated and mother plants.

Rapid karyotypic evolution with high diploid number variation in a rare genus of bromeligenous frogs.

Bromeligenous Crossodactylodes is a leptodactylid genus closely related to Paratelmatobius and Scythrophrys. The diploid number in all karyotyped species of these two latter genera is 24, which diverges from the modal diploid number (2n = 22) in the family. Here, we analyzed three species of Crossodactylodes and found karyotypes with 2n = 30, 2n = 32, and 2n = 36, diploid numbers that have not been reported in any other diploid leptodactylid species to date. Reconstruction of the ancestral chromosome number indicated that the diploid number changed from 22 to 24 in the common ancestor of Crossodactylodes, Paratelmatobius, and Scythrophrys, and that progressive increases in diploid number have occurred in Crossodactylodes. The large number of telocentric/subtelocentric chromosomes in karyotypes with higher diploid numbers raises the possibility that centric fissions may have occurred during the evolution of Paratelmatobiinae. Three metacentric chromosomes, probably involved in fission events, were inferred to be present in the common ancestor of all species of Crossodactylodes, but in C. bokermanni. Chromosome mapping of the satellite DNA PcP190 suggests homology between one arm of metacentric chromosome 1 of Crossodactylodes sp. 3 and telocentric chromosome 2 of C. itambe, supporting one of the presumed centric fission events.

Phylogenetic Reconstruction of the Ancestral Chromosome Number of the Genera Anochetus Mayr, 1861 and Odontomachus Latreille, 1804 (Hymenoptera: Formicidae: Ponerinae)

Recent phylogenetic and molecular data are changing our knowledge about the relations between species and evolutionary processes resulting in the chromosome variation observed in ants (Hymenoptera: Formicidae). Ants exhibit remarkable variations in morphology, behavior, karyotypes, and chromosome structure. By assembling genetic and chromosome information about the trap-jaw ants from the subfamily Ponerinae, we reconstructed the phylogenetic relationships that inferred the monophyletic condition between the Anochetus and Odontomachus genera and estimated their ancestral haploid chromosome number. According to our inferences, these clades have an ancestral haploid chromosome number n = 15. The most recent common ancestor of Anochetus and Odontomachus has arisen between the Early Paleocene and the Early Eocene periods (time of the most recent common ancestor). In the Anochetus genus, we observed maintenance of the ancestral chromosome number estimated here in most species. This also suggests that pericentric inversions were the primary chromosomal rearrangement modulating the karyotype evolution of this genus. However, a reduction from n = 15–14 is observed in Anochetus emarginatus and Anochetus cf. madaraszi, which likely occurred by centromeric fusion. In contrast, the increase from the ancestral karyotype number in Anochetus horridus suggested centromeric fissions. Odontomachus showed maintenance of the ancestral chromosome number in the “rixosus group” and several gains in all species from the “haematodus group.” Our findings suggest that centromeric fissions and pericentric rearrangements lead to chromosomal changes in trap-jaw ants. Considering the ancestral state estimated here, changes in chromosome morphology are likely due to pericentric inversions, and chromosome number increases are likely due to centric fissions. The higher number of acrocentric or telocentric chromosomes in the karyotypes with n < 15 haploid chromosomes supports such an idea.