Differences In Chromosome Size Research Articles

Chromosome size affects alignment efficiency in mammalian mitosis.

The kinetochore connects chromosomes to spindle microtubules during cell division. Accurate chromosome segregation requires sister kinetochores to biorient, attaching to opposite spindle poles. To achieve biorientation, the kinetochore destabilizes incorrect attachments and stabilizes correct ones. How it discriminates correct from incorrect attachments is not clear. Here, we test the model that tension serves as the stabilizing cue at correct attachments and how that model affects chromosomes of different sizes. Live imaging of mitotic PtK2 cells reveals long chromosomes align at the metaphase plate more slowly than short chromosomes. Using laser ablation to shorten long chromosome arms—reducing polar ejection forces on them—we show that chromosomes align faster after ablation, indicating chromosome size affects alignment efficiency. Finally, artificially enriching for incorrect attachments using STLC washouts and imaging error correction live, we show that long chromosomes exhibit a delay in correcting errors, rather than simply in attachment formation. We propose a model where increased polar ejection forces on long chromosomes stabilize not only correct but also incorrect attachments, delaying their biorientation and alignment. As such, long chromosomes may experience more challenges correcting errors and, as a result, higher missegregation rates.

Linked-Read Sequencing of Eight Falcons Reveals a Unique Genomic Architecture in Flux.

Falcons are diverse birds of cultural and economic importance. They have undergone major lineage-specific chromosomal rearrangements, resulting in greatly reduced chromosome counts relative to other birds. Here, we use 10X Genomics linked reads to provide new high-contiguity genomes for two gyrfalcons, a saker falcon, a lanner falcon, three subspecies of peregrine falcons, and the common kestrel. Assisted by a transcriptome sequenced from 22 gyrfalcon tissues, we annotate these genomes for a variety of genomic features, estimate historical demography, and then investigate genomic equilibrium in the context of falcon-specific chromosomal rearrangements. We find that falcon genomes are not in AT–GC equilibrium with a bias in substitutions toward higher AT content; this bias is predominantly but not exclusively driven by hypermutability of CpG sites. Small indels and large structural variants were also biased toward insertions rather than deletions. Patterns of disequilibrium were linked to chromosomal rearrangements: falcons have lost GC content in regions that have fused to larger chromosomes from microchromosomes and gained GC content in regions of macrochromosomes that have translocated to microchromosomes. Inserted bases have accumulated on regions ancestrally belonging to microchromosomes, consistent with insertion-biased gene conversion. We also find an excess of interspersed repeats on regions of microchromosomes that have fused to macrochromosomes. Our results reveal that falcon genomes are in a state of flux. They further suggest that many of the key differences between microchromosomes and macrochromosomes are driven by differences in chromosome size, and indicate a clear role for recombination and biased gene conversion in determining genomic equilibrium.

Chromosome size affects sequence divergence between species through the interplay of recombination and selection.

The structure of the genome shapes the distribution of genetic diversity and sequence divergence. To investigate how the relationship between chromosome size and recombination rate affects sequence divergence between species, we combined empirical analyses and evolutionary simulations. We estimated pairwise sequence divergence among 15 species from three different mammalian clades—Peromyscus rodents, Mus mice, and great apes—from chromosome‐level genome assemblies. We found a strong significant negative correlation between chromosome size and sequence divergence in all species comparisons within the Peromyscus and great apes clades but not the Mus clade, suggesting that the dramatic chromosomal rearrangements among Mus species may have masked the ancestral genomic landscape of divergence in many comparisons. Our evolutionary simulations showed that the main factor determining differences in divergence among chromosomes of different sizes is the interplay of recombination rate and selection, with greater variation in larger populations than in smaller ones. In ancestral populations, shorter chromosomes harbor greater nucleotide diversity. As ancestral populations diverge, diversity present at the onset of the split contributes to greater sequence divergence in shorter chromosomes among daughter species. The combination of empirical data and evolutionary simulations revealed that chromosomal rearrangements, demography, and divergence times may also affect the relationship between chromosome size and divergence, thus deepening our understanding of the role of genome structure in the evolution of species divergence.

Chromosome change and karyotype differentiation–implications in speciation and plant systematics

Karyotype characterizing the phenotypic aspects of the chromosome complement represents structural and functional organization of the nuclear genome. Its constancy ensures transfer of the same genetic material to the next generation, while variation enables ecological differentiation and adaptation. Superimposition of karyotype information onto a phylogenetic framework has immense utility in elucidating direction of evolutionary change and delineation of taxonomic hierarchy. This article attempts to provide an illustrated description of the chromosomal features that are useful in discerning differences and affinities between species and taxa. A detailed account of experimental parameters useful in chromosome identification and evaluation of karyotype asymmetry is furnished citing suitable examples. In addition to various karyotypic indices, special emphasis is given to the quantitative parameter of “chromosome dispersion index (DI)” that promises phylogenetic differentiation of closely related karyotypes, since most genera of herbaceous angiosperms display interspecific differences in chromosome size and symmetry, if not number. Karyo-evolutionary trends involve both change in chromosome number, morphology/karyotype symmetry, ploidy and total haploid length. The pattern of DNA addition/deletion across the chromosome complement has been found to be variable. Such change in DNA is either equally shared by all the chromosomes or is proportionately shared commensurate to chromosome size, leading to differential pace of change in karyotype asymmetry across the taxa. The large data accumulating on chromosome number over the years offer opportunities to utilize them as additional tools in taxonomy. The basic chromosome number (ancestral haploid number) in angiosperms has been suggested as n = 7, and an ancestral 1C of 1.73 pg, which is characteristic of the major groups with slight deviation in certain orders. The average ‘holoploid genome size’ i.e. 1C, for the Angiosperms is inferred to be 5870 Mb/6.0 pg. However, the 1C-value data available for ca.10800 species of Angiosperms reveal genome size diversity ranging from 61 Mb/0.0648 pg in the carnivorous plant Genlisea tuberosa (Lentibulariaceae) to 1,49,000 Mb/152.23 pg in Paris japonica (Melanthiaceae) suggesting over 2400 fold variation across the angiosperms; and 230 fold variation within the family (0.66 pg in Schoenocaulon texanum vs. P. japonica with highest C value). Metaphase chromosome size is estimated to range from the shortest ~ 0.3 µm in Genlisea aurea, and at family level from ~ 0.8 µm in Chamaelirium luteum to ~ 30 µm in Paris japonica. Chromosome number ranges from n = 2 to 320 across the angiosperms, at family level from n = 4 to 120 in the Brassicaceae, and at genus level from n = 2 to 45 in Brachyscome (Compositae).The evolution has mostly been at the diploid level. It is generally believed that the chromosome size of monocots is larger than dicots and the chromosome size of temperate plants is larger than tropical plants. For a broader sense and larger scale understanding, the evolutional conception of karyotype is principally based on the thoughts that: (i) symmetrical karyotype is more primitive than asymmetrical ones, (ii) longer chromosomes are primitive than shorter ones, (iii) median centromeres with chromosome arms of equal length are more primitive than chromosome arms of unequal length, (iv) low basic numbers had given rise to higher ones, and the taxa with variable chromosome number are considered young and still in evolutionary flux, (v) species with one NOR site per haploid genome are considered advanced than multiple NOR sites, (vi) ancient species had less heterochromatin (repetitive DNA), the primitive species accredited heterochromatin, followed by gradual shedding of excess heterochromatin with evolutionary specialization. However, discovery of ancient episodes of Whole Genome Duplication (WGD) events said to have happened as an escape to the 5th mass extinction at the end of Cretaceous as a survival strategy has opened newer possibilities. A new thinking is beginning to emerge that concomitant with the climate change happening at a fast pace in the Anthropocene, it is likely that if global climate undergoes major change in coming centuries then auto-polyploidization could be the important player leading to increase in chromosome number.

B Chromosomes and Cytogenetic Characteristics of the Common Nase Chondrostoma nasus (Linnaeus, 1758).

Supernumerary B chromosomes (Bs) are very promising structures, among others, in that they are an additional genomic compartment for evolution. In this study, we tested the presence and frequency of B chromosomes and performed the first cytogenetic examination of the common nase (Chondrostoma nasus). We investigated the individuals from two populations in the Vistula River basin, in Poland, according to the chromosomal distribution of the C-bands and silver nucleolar organizer regions (Ag-NORs), using sequential staining with AgNO3 and chromomycin A3 (CMA3). Furthermore, we analyzed the chromosomal localization of two rDNA families (45S and 5S rDNA) using fluorescence in situ hybridization (FISH) with rDNA probes. Chondrostoma nasus individuals showed a standard (A) chromosome set consisting of 2n = 50: 12 metacentric, 32 submetacentric, and 6 acrocentric chromosomes (NF = 94). Fourteen out of the 20 analyzed individuals showed 1–2 mitotically unstable submetacentric B chromosomes of different sizes. Six of them, in 14.1% of the analyzed metaphase plates, had a single, medium-sized submetacentric B (Bsm) chromosome (2n = 51) with a heterochromatic block located in its pericentromeric region. The other seven individuals possessed a Bsm (2n = 51) in 19.4% of the analyzed metaphase plates, and a second Bsm chromosome (2n = 52), the smallest in the set, in 15.5% of metaphase plates, whereas one female was characterized by both Bsm chromosomes (2n = 52) in 14.3% of the analyzed metaphase plates. AgNORs, GC-rich DNA sites, and 28S rDNA hybridization sites were observed in the short arms of two submetacentric chromosome pairs of A set. The constitutive heterochromatin was visible as C bands in the centromeric regions of almost all Chondrostoma nasus chromosomes and in the pericentromeric region of several chromosome pairs. Two 5S rDNA hybridization sites in the pericentromeric position of the largest acrocentric chromosome pair were observed, whereas two other such sites in co-localization on a smaller pair of NOR chromosomes indicate a species-specific character. The results herein broaden our knowledge in the field of B chromosome distribution and molecular cytogenetics of Chondrostoma nasus: a freshwater species from the Leuciscidae family.

Evolution of the parthenogenetic rock lizard hybrid karyotype: Robertsonian translocation between two maternal chromosomes in Darevskia rostombekowi.

Darevskia rostombekowi, the most outstanding of the seven known parthenogenetic species in the genus Darevskia, is the result of an ancestral cross between two bisexual species Darevskia raddei and Darevskia portschinskii. The chromosomal set of this species includes a unique submetacentric autosomal chromosome; the origin of this chromosome was unresolved as only acrocentric chromosomes are described in the karyotypes of Darevskia genus normally. Here, we applied a suite of molecular cytogenetic techniques, including the mapping of telomeric (TTAGGG) n repeats using fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH), and whole-chromosome painting (WCP) in both D. rostombekowi and parental (D. portschinskii and D. raddei) species. The obtained results in total suggest that a de novo chromosomal rearrangement via Robertsonian translocation (centric fusion) between two maternal (D. raddei) acrocentric chromosomes of different size was involved in the formation of this unique submetacentric chromosome present in the parthenogenetic species D. rostombekowi. Our findings provide new data in specific and rapid evolutional processes of a unisexual reptile species karyotype.

Karyotypic Divergence of Two Co-Occurring Species of Andean Climbing Catfishes (Siluriformes: Loricarioidei: Astroblepidae).

The monotypic Astroblepidae fish family includes 81 species distributed along Central and Northern Andes in South America and Panamá in Central America; most aspects regarding its biology, taxonomy, and chromosomal features remain largely unknown. This study reports the karyotype of two sympatric Astroblepus species from the Colombian Andes, aiming to provide novel information on karyotype organization and reveal possible chromosomal rearrangements occurred on these species, through mapping of different repetitive DNA classes, including microsatellites and ribosomal DNA multigene families. The results showed differences in the chromosome number and karyotypic formula: Astroblepus grixalvii had 2n = 52 (28m+8sm +12st +4a) with the metacentric pair number 1 as the largest chromosome pair, whereas Astroblepus homodon had 2n = 54 (30m+8sm +8st +8a) and less evident chromosome size differences. Microsatellite probes marked the tips of all chromosomes in both species except the short arms of acrocentric pair numbers 24 and 25 in A. homodon. Each ribosomal probe marked different chromosome pairs in both species. Microsatellite patterns suggest that the 2n increase probably involved a centric fission event that occurred during the evolutionary history of these species. This is the first karyotype description of an Astroblepus species and it contributes to the theoretical framework about the karyoevolutionary trends within Loricarioidei.

Synchronous termination of replication of the two chromosomes is an evolutionary selected feature in Vibrionaceae.

Vibrio cholerae, the causative agent of the cholera disease, is commonly used as a model organism for the study of bacteria with multipartite genomes. Its two chromosomes of different sizes initiate their DNA replication at distinct time points in the cell cycle and terminate in synchrony. In this study, the time-delayed start of Chr2 was verified in a synchronized cell population. This replication pattern suggests two possible regulation mechanisms for other Vibrio species with different sized secondary chromosomes: Either all Chr2 start DNA replication with a fixed delay after Chr1 initiation, or the timepoint at which Chr2 initiates varies such that termination of chromosomal replication occurs in synchrony. We investigated these two models and revealed that the two chromosomes of various Vibrionaceae species terminate in synchrony while Chr2-initiation timing relative to Chr1 is variable. Moreover, the sequence and function of the Chr2-triggering crtS site recently discovered in V. cholerae were found to be conserved, explaining the observed timing mechanism. Our results suggest that it is beneficial for bacterial cells with multiple chromosomes to synchronize their replication termination, potentially to optimize chromosome related processes as dimer resolution or segregation.

CHROMOSOMAL ABNORMALITIES SHEEP

Successful and creative plant-breeding work in a stock-raising is based on the estimation of genetic potential of separate breeds, herds and individuals, that is impossible without thorough genetic- populations knowledge. Knowledge of features of caryotype gives an opportunity objectively to estimate the breeds of animals taking into account their population-cytogenetic features, that assists more complete idea about the evolution of breeds. However such important agricultural object, as a domestic sheep, remains cytogenetic poorly studied, especially in a population-cytogenetic aspect.In literature different breeds have small information about frequency and spectrum of the inherited anomalies and populations of sheep. Most chromosomal and genic anomalies of sheep in general not research, although for practice of plant-breeding work necessary knowledge of reasons of their appearance. Caryotype of sheep is presented by 54 chromosomes, from them 26 pairs of autsom and one pair of sexual chromosomes (ХХ or ХУ). Three pairs of large metacentric and 23 pairs of acrocentric chromosomes of different size enter in the complement of autsom. For sheep as well as for other animals characteristic chromosomal polymorphism as a numerical varying of chromosomes in caryotype (aneuploidi and poliploidi), morphological aberations and associations of separate chromosomes. Chromosomal anomalies of sheep are reason of forming of nonviable gamet, that results in death of embryos on the early stages, and, as a result, to the considerable economic losses in economies. The facts of chromosomal aberation educed for sheep testify to the necessity of cytogenetic control of tribal animals, especially rams, with the aim of exposure of animals-transmitters of undesirable changes in caryotype and exception of them from a plant-breeding process.

Chromosome numbers of five Turkish Centaurea L. (Asteraceae) species

We investigated the chromosome number and morphology of five Centaurea species belonging to five different Centaurea sections. All material analyzed was diploid with chromosome number 2n = 18 or 2n = 20. Chromosome number 2n = 18 was found for two populations (specimen a and specimen b) of Centaurea cassia Boiss., a rare species from Sect. Jacea (Mill.) DC., and two populations (specimen a and specimen b) of C. ptosimopappa Hayeka, a local endemic belonging to Sect. Ptosimopappus O. Hoffm. A chromosome number of 2n = 20, however, was observed for the other three Centaurea species: C. arifolia Boiss., a local endemic from Sect. Cynaroides Boiss. ex Walp., C. antochia Boiss. var. antochia, an endemic variety belonging to Sect. Acrocentron (Cass.) DC., and C. hyalolepis Boiss. from Sect. Calcitrapa DC. The chromosome number for the latter species represents the first record for Hatay province. Differences in chromosome size and karyotype are described.

Molecular phylogeny and chromosome evolution among the creeping herbaceous Oxalis species of sections Corniculatae and Ripariae (Oxalidaceae)

Oxalis sections Corniculatae DC. and Ripariae Lourteig are composed mainly of creeping herbs. They not only share strong morphological similarities, such as the presence of a reptant stem but also some cytogenetic characteristics. Several species in section Corniculatae share a base chromosome number x=5 with species in section Ripariae, while other species in the former have a x=6. We used a molecular and cytogenetic approach to determine the phylogenetic relationships, test the previous taxonomic classification and study the genome rearrangements that led to the differences in chromosome size and basic chromosome number between both sections. Phylogenetic relationships were inferred based on DNA sequences from chloroplast and nuclear ribosomal ITS. The molecular phylogenetic analyses found that neither of the sections are monophyletic, but do support two clades. The first group contains diploid species with x=5, large chromosomes and high DNA content and the second diploid and polyploidy species with x=6, small chromosomes and low DNA content. The x=5 clade comprises species of both sections, while the x=6 clade was formed mainly by section Corniculatae species and O. serpens from section Ripariae. Our results suggest that x=5 and high DNA content are derived conditions, which may have resulted from descendent disploidy and proliferation of transposable elements. Thus, cytogenetic data superimposed on the phylogeny have shown two different modes of chromosome evolution in both lineages: (1) chromosome rearrangements and increase in genome size in the x=5 lineage and (2) polyploidy playing the main role in chromosome evolution among species in the x=6 species. A taxonomic revision for the two sections is suggested.

Rice structural variation: a comparative analysis of structural variation between rice and three of its closest relatives in the genus Oryza

Rapid progress in comparative genomics among the grasses has revealed similar gene content and order despite exceptional differences in chromosome size and number. Large- and small-scale genomic variations are of particular interest, especially among cultivated and wild species, as they encode rapidly evolving features that may be important in adaptation to particular environments. We present a genome-wide study of intermediate-sized structural variation (SV) among rice (Oryza sativa) and three of its closest relatives in the genus Oryza (Oryza nivara, Oryza rufipogon and Oryza glaberrima). We computationally identified regional expansions, contractions and inversions in the Oryza species genomes relative to O. sativa by combining data from paired-end clone alignments to the O. sativa reference genome and physical maps. A subset of the computational predictions was validated using a new approach for BAC size determination. The result was a confirmed catalog of 674 expansions (25-38 Mb) and 611 (4-19 Mb) contractions, and 140 putative inversions (14-19 Mb) between the three Oryza species and O. sativa. In the expanded regions unique to O. sativa we found enrichment in transposable elements (TEs): long terminal repeats (LTRs) were randomly located across the chromosomes, and their insertion times corresponded to the date of the A genome radiation. Also, rice-expanded regions contained an over-representation of single-copy genes related to defense factors in the environment. This catalog of confirmed SV in reference to O. sativa provides an entry point for future research in genome evolution, speciation, domestication and novel gene discovery.

Chromosome Size Differences May Affect Meiosis and Genome Size

Genetic crosses in many organisms have shown that alleles of unlinked genes generally assort independently of one another during gamete formation. However, variation in chromosome size may affect the process of meiosis and lead to nonindependent assortment of chromosomes. We therefore examined chromosomes with insertions and found that they preferentially segregated away from the X chromosome during meiosis in Caenorhabditis elegans males. Conversely, chromosomes with deletions preferentially segregated with the X chromosome. The degree of segregation bias was significantly associated with the length of the insertion or deletion. Simulations revealed that this segregation bias leads to genome size reduction in hermaphroditic species, a pattern consistent with differences in genome sizes in the genus Caenorhabditis. These results suggest that insertions and deletions may affect chromosome segregation patterns.

Cytogenetics of three species of scorpions of the genus Brachistosternus from Argentina (Scorpiones: Bothriuridae)

Meiotic studies on three phylogenetically distant species of the genus Brachistosternus Pocock from Argentina were conducted. One species is from the subgenus Ministernus Francke 1985, B. ferrugineus Thorell 1876, and two species are from the subgenus Brachistosternus Pocock 1893, B. montanus Roig-Alsina 1977 (Andean species group), and morphologically different populations of B. pentheri Mello-Leitão 1931 (plains species group). All species showed achiasmatic meiosis, absence of heteromorphic bivalents, and bibrachial and monobrachial chromosomes of different sizes. Males of Brachistosternus ferrugineus, B. montanus, and one population of B. pentheri have 2n = 46. Males of the typical populations of B. pentheri have 2n = 42. These results suggest that B. pentheri may comprise two species.

The New WorldArtemiaspeciesA. franciscanaandA. persimilisare highly differentiated for chromosome size and heterochromatin content

Chromosomal rearrangements have played a key role in the speciation of the New World sexual Artemia species (Crustacea, Anostraca) A. franciscana and A. persimilis. The species differ by a chromosome duplication (2n+2=44 in A. persimilis vs 2n=42 in A. franciscana), and a greater amount of heterochromatin (HCH) in A. franciscana. To investigate this difference in HCH, four parameters were compared for the first time in Artemia: 1) the absolute sizes of one A. persimilis and four A. franciscana karyotypes; 2) the relative lengths of all chromosome; 3) the number of heterochromatic bands and 4) the relative amounts of HCH per chromosome and its position. The two A.franciscana karyotypes with the largest HCH amount (26%), have twice (139.26 microm and 134.05 microm) the absolute size of the A.persimilis karyotype (64.91 microm; HCH: 1.97%). Interspecific and intraspecific (A. franciscana) differences in chromosome size and HCH were observed, although the two sets of information are not positively correlated. While A. persimilis shares plesiomorphic karyological traits with Old World species, A. franciscana has apomorphic features such as longer chromosomes and greater HCH content, mainly dispersed towards telomeres. The impacts of such chromosome rearrangements are discussed in relation to the wider geographic distribution, greater colonizing ability, and life history plasticity of A. franciscana. An additional, though preliminary, point of this paper is the observation that the female would be the heterogametic sex.

Differential replication dynamics for large and small Vibrio chromosomes affect gene dosage, expression and location

BackgroundReplication of bacterial chromosomes increases copy numbers of genes located near origins of replication relative to genes located near termini. Such differential gene dosage depends on replication rate, doubling time and chromosome size. Although little explored, differential gene dosage may influence both gene expression and location. For vibrios, a diverse family of fast growing gammaproteobacteria, gene dosage may be particularly important as they harbor two chromosomes of different size.ResultsHere we examined replication dynamics and gene dosage effects for the separate chromosomes of three Vibrio species. We also investigated locations for specific gene types within the genome. The results showed consistently larger gene dosage differences for the large chromosome which also initiated replication long before the small. Accordingly, large chromosome gene expression levels were generally higher and showed an influence from gene dosage. This was reflected by a higher abundance of growth essential and growth contributing genes of which many locate near the origin of replication. In contrast, small chromosome gene expression levels were low and appeared independent of gene dosage. Also, species specific genes are highly abundant and an over-representation of genes involved in transcription could explain its gene dosage independent expression.ConclusionHere we establish a link between replication dynamics and differential gene dosage on one hand and gene expression levels and the location of specific gene types on the other. For vibrios, this relationship appears connected to a polarisation of genetic content between its chromosomes, which may both contribute to and be enhanced by an improved adaptive capacity.

Intrapopulation Genome Size Dynamics in Festuca pallens

It is well known that genome size differs among species. However, information on the variation and dynamics of genome size in wild populations and on the early phase of genome size divergence between taxa is currently lacking. Genome size dynamics, heritability and phenotype effects are analysed here in a wild population of Festuca pallens (Poaceae). Genome size was measured using flow cytometry with DAPI dye in 562 seedlings from 17 maternal plants varying in genome size. The repeatability of genome size measurements was verified at different seasons through the use of different standards and with propidium iodide dye; the range of variation observed was tested via analysis of double-peaks. Additionally, chromosome counts were made in selected seedlings. Analysis of double-peaks showed that genome size varied up to 1.188-fold within all 562 seedlings, 1.119-fold within the progeny of a single maternal plant and 1.117-fold in seedlings from grains of a single inflorescence. Generally, genome sizes of seedlings and their mothers were highly correlated. However, in maternal plants with both larger and smaller genomes, genome sizes of seedlings were shifted towards the population median. This was probably due to the frequency of available paternal genomes (pollen grains) in the population. There was a stabilizing selection on genome size during the development of seedlings into adults, which may be important for stabilizing genome size within species. Furthermore, a positive correlation was found between genome size and the development rate of seedlings. A larger genome may therefore provide a competitive advantage, perhaps explaining the higher proportion of plants with larger genomes in the population studied. The reason for the observed variation may be the recent induction of genome size variation, e.g. by activity of retrotransposons, which may be preserved in the long term by the segregation of homeologous chromosomes of different sizes during gametogenesis.

Giemsa C-banded karyotypes of three subspecies of Taeniatherum caput-medusae and of two intergeneric hybrids with Psathyrostachys spp. (Poaceae)

Three subspecies of Taeniatherum caput-medusae (2n=2x=14) had the same karyotype with five pairs of metacentrics, one pair of submetacentrics, and one pair of metacentric SAT-chromosomes with small satellites. The rather similar C-banded karyotypes were characterized by banding patterns with a limited number of mostly small or very small bands randomly distributed. Plants of the same population had identical banding patterns. Banding pattern polymorphism was prevalent, but apparently no larger among than within taxa. The similarity of the C-banded karyotypes supports a close relationship of taxa. Differences in chromosome size and C-banding patterns identified parental genomes in two Taeniatherum×Psathyrostachys hybrids. Psathyrostachys SAT-chromosomes exerted nucleolar dominance. A hierarchy of nucleolar dominance: Hordeum vulgare > P. fragilis > T. caput-medusae is indicated.

Supernumerary ring chromosomes accompanied with near-tetraploidy following chemotherapy and cranial radiation in a girl with a relapsed acute lymphoblastic leukemia

Supernumerary ring chromosomes of different sizes and near-tetraploidy were presented in the bone marrow cells of 12-year-old girl with relapsed acute lymphoblastic leukemia who had been treated previously with chemotherapy and cranial radiation. Despite significant chromosomal abnormalities, complete hematologic and cytogenetic remissions were achieved.

Molecular cloning of Tulipa fosteriana rDNA and subsequent FISH analysis yields cytogenetic organization of 5S rDNA and 45S rDNA in T. gesneriana and T. fosteriana

In this study, Tulipa fosteriana was found to contain 45S rDNA repeat units of 9.7 and 9.5 kb, in which at least 7 types of 45S rDNAs were identified by restriction site analysis. For 5S rDNA, repeat units ranging from 364 bp to 396 bp were identified. The diploid cultivars (2n = 2x = 24) ‘Christmas Dream’ and ‘Queen of Night,’ representing the horticultural group T. gesneriana, and ‘Red Emperor’, belonging to T. fosteriana, were compared cytogenetically using cloned 5S and 45S rDNAs. Fluorescence in situ hybridization (FISH) analysis identified many rDNA sites located on each chromosome in the diploid genomes. For example, we identified 71 sites of 5S rDNA and 10 sites of 45S rDNA in ‘Red Emperor’. Additionally, FISH analyses enabled construction of karyotypes for these cultivars. Karyotype comparison of T. gesneriana cultivars showed conservation of repetitive rDNA unit positioning. A clear difference in chromosome size and signal pattern was observed between T. gesneriana and T. fosteriana cultivars. Here we demonstrate the unique nature of the highly repeated 5S rDNA units in these Tulipa species and the usefulness of FISH karyotyping with cloned 5S and 45S rDNAs to clearly distinguish between chromosomes from T. gesneriana and T. fosteriana.