Total Chromosome Volume Research Articles

Near millimolar concentration of nucleosomes in mitotic chromosomes from late prometaphase into anaphase.

Chromosome compaction is a key feature of mitosis and critical for accurate chromosome segregation. However, a precise quantitative analysis of chromosome geometry during mitotic progression is lacking. Here, we use volume electron microscopy to map, with nanometer precision, chromosomes from prometaphase through telophase in human RPE1 cells. During prometaphase, chromosomes acquire a smoother surface, their arms shorten, and the primary centromeric constriction is formed. The chromatin is progressively compacted, ultimately reaching a remarkable nucleosome concentration of over 750 µM in late prometaphase that remains relatively constant during metaphase and early anaphase. Surprisingly, chromosomes then increase their volume in late anaphase prior to deposition of the nuclear envelope. The plateau of total chromosome volume from late prometaphase through early anaphase described here is consistent with proposals that the final stages of chromatin condensation in mitosis involve a limit density, such as might be expected for a process involving phase separation.

Intraspecific karyomorphological and genome size variations of in vitro embryo derived Iranian endemic Asafoetida (Ferula assa-foetida L., Apiaceae)

Asafoetida (Ferula assa-foetida L.) is one of the endemic medicinal plants in Iran. Analysis of karyomorphology and 2Cx DNA measurements (monoploid genome size) of 18 Iranian endemic Ferula assa-foetida populations were performed. The in vitro embryo-derived root tips were examined for karyological studies, via technique of squash and stain with 2% (w/v) aceto-orcein. Seeds of the Ferula samples and leaves of Solanum lycopersicum as standard reference (2C DNA = 1.96 pg) were stained with propidium iodide (PI), using flow cytometric (FCM) technique. All the studied populations were diploids (2n = 2x = 22) with mean chromosome length (CL) of 3.95 μm, varied from 3.05 μm (P7) to 4.94 μm (P18). The mean total chromosome volume (TCV) was 0.98 μm3, ranged from 0.47 μm3 (P7) to 1.57 μm3 (P3). Two-typed chromosomes (“m”, “sm”) formed three classes of karyotype formula. Karyotypes were mostly symmetrical and fell in 1A and 2A Stebbins category. The monoploid genome size of Iranian endemic Ferula assa-foetida populations is being stated for the first time; its mean value was 4.51 pg, ranged from 4.09 (P4) to 4.69 pg (P16). Intraspecific karyomorphological and genome size variations were clearly confirmed in studied Ferula assa-foetida.

Interspecific Genome Size Variation of Iranian Endemic <i>Allium</i> Species (Amaryllidaceae)

The genus Allium L. is in Amaryllidaceae family with approximately 900 species distributed worldwide. The key aim of this study was to examine variations among eight Iranian endemic Allium species based on genome size. The results showed that among eight Allium species examined, seven were diploid (A. sativum, A. stipitatum, A. fistolosum, A. umbellicatum, A. lenkoranicum, A. stamineum, and A. rubellum; 2n=2x=16). Interestingly, the chromosome number 2n=3x=24 was evidenced in A. atroviolaceum. Strong interspecific diversity was identified in the studied Allium genome size. The overall average genome sizes of examined species were 34.17 pg, varying from 22.24 pg in A. fistolosum to 43.80 pg in A. stipitatum. The positive and significant correlations between genome size and total chromosome volume (TCV), altitude, and latitudes indicate that the species with larger genome sizes were situated in higher sea levels and low latitudes areas. These results may provide suitable information for Allium evolutionary, genetics, and breeding studies.

Karyotype Variation in Eight Cultivars of Indian Dessert Banana (Musa acuminata L.) of Section Eumusa From Odisha, India

Banana (Musa spp.) cultivars especially dessert banana are important cash crop with high market demand all over the world as an integral part of the diet. The need for assessment of cytogenetic characters in Musa cultivars is inevitable as out of thousands of cultivars, cytogenetic characterization of most of them remains unresolved due to difficulties like small chromosome size, diversity in ploidy levels and high cultivar diversity which behave differently to standardized cytogenetic protocols. In this report, somatic chromosome number, detailed karyotype analysis including total chromosome length, volume, form percentage, Interphase Nuclear Volume (INV) were accessed on eight dessert type of Musa accessions from different places of Odisha. All the cultivars studied were found triploid (2n = 33) with a basic chromosome number of x=11. The karyotype formulae were assigned to each cultivar by grouping the chromosome according to their shared characteristics. The total chromosome length ranged from 54.95 µm in cv. Robusta to 81.5 µm in cv. Kathia with symmetric karyotype in all the studied cultivar. Karyotype formula revealed structural alteration of chromosome with Total Form percentage (TF%) variation from 35.65% in cv. Amritapani to 41.68% in cv. Patakpura that confirms more number of nearly median constricted chromosome as compared to sub-median chromosome. The total chromosome volume recorded from 10.78 µm3 in cv. Robusta to 15.99 µm3 in cv. Khatia and the INV varied from 1336.44 µm3 in cv. Dwarf Cavendish to 2048.37 µm3 in cv. Patakpura. The recorded structural variation might be due to differential genome specific condensation of chromosome. Chromosome length and volume found statistically significant among the cultivars.

Karyological and flow cytometric studies of Tulipa (Liliaceae) species from Iran

Chromosomal and karyotype parameters and genome size were examined in 22 Iranian populations of nine different Tulipa species, using squash technique and 1 % (w/v) aceto-orcein stain. Flow cytometric studies were performed using PI staining method and Vicia faba cv. Inovec (2C DNA = 26.9 pg) as a reference standard. Most species were diploid (2n = 2x = 24), having three chromosome types (“m”, “sm”, “st”). The chromosome length (TL) varied from 6.4 μm (S2) to 12.90 μm (S3). Total chromosome volume (TCV) ranged from 32.9 μm3 (S2) to 66.0 μm3 (S8). Statistical analyses confirmed more intraspecific chromosomal and genome size variations than interspecific. S1E2, S2E1 and S5E2, with the highest intrachromosomal (M CA) and relatively high interchromosomal asymmetry (CVCL), indicated higher asymmetry in the karyotype. The genome size in Tulipa species of Iran is being reported for the fist time. The mean 2C DNA was 54.52 pg, and ranged from 77.40 in S6E2 to 31.51 pg in S9E2. Significant positive correlations were found between 2C DNA and either TL or TCV.

A method of standardization of chromosome length measurement

Chromosome length is a basic karyotype characteristic. This paper shows, on the basis of total chromosome length (TCL) measurement, that this value is not a stable one. TCL varies among different c-metaphases from one meristem; the average TCL is different for (a) different pre-treatment agents; (b) different pre-treatment times for the same pre-treatment agents; and (c) between siblings treated simultaneously. In the same way, total chromosome volume (TCV) is not a suitable characteristic for chromosome size comparison. To solve the problem of chromosome size comparison the following standardization of TCL measurement is proposed: to determine TCL in c-metaphases with the chromosomes contracted to maximum level and still retaining all measurable karyotype characteristics. This way of standardization requires a pre-treatment method providing c-metaphases suitable for standardized TCL measurement. The paper also brings one new chromosome number to science: Onosma thracica, 2n = 14.

Karyotypic and Nuclear DNA Variations inLathyrus sativus(Fabaceae)

Karyotypic studies were performed on 20 grasspea (Lathyrus sativus L.) genotypes (15 genotypes from ICARDA and 5 from Iran) labeled G1-G20. All genotypes examined were diploid (2n = 2x = 14), having mean chromosome length (TL) of 6.03 µm (4.7-6.7 µm) and total chromosome volume mean (TCV) of 24.2 µm 3 (18.1-35.1 µm 3 ). The largest value of chromatin length was detected on G8 (93.3 µm) while G3 demonstrated the smallest value (65.2 µm). Karyotype formula was determined as 14m in 19 genotypes and 12m + 2sm in G20, using LEVAN et al. chromosome nomenclature. Satellite numbers varied between 1 to 2 pairs. Karyotypes were classifi ed as 1A of STEBBINS classifi cation. The scatter diagram of A1 and A2 asymmetry indicated 5 groups of genotypes: G2 and G19 with the most asymmetrical and symmetrical karyotypes, respectively. Results of multivariate analysis and scatter diagram of TL with CI indicated 3 groups of genotypes according to their chro- mosomal parameters. Flow cytometric studies were performed, using PI staining method and Pisum sativum cv. Ctirad (2C DNA = 9.09 pg) as a reference standard. The mean 2C DNA content of all genotypes was 14.7 pg, ranging from 13.8 pg (G1) to 15.6 pg (G20). Signifi cant positive correlations were found between 2C DNA content and either stomatal cell area or longitude.

Genome size variation in Begonia

The genome sizes of a Begonia collection comprising 37 species and 23 hybrids of African, Asiatic, Middle American, and South American origin were screened using flow cytometry. Within the collection, 1C values varied between 0.23 and 1.46 pg DNA. Genome sizes were, in most cases, not positively correlated with chromosome number, but with pollen size. A 12-fold difference in mean chromosome size was found between the genotypes with the largest and smallest chromosomes. In general, chromosomes from South American genotypes were smaller than chromosomes of African, Asian, or Middle American genotypes, except for B. boliviensis and B. pearcei. Cytological chromosome studies in different genotypes showed variable chromosome numbers, length, width, and total chromosome volume, which confirmed the diversity in genome size. Large secondary constrictions were present in several investigated genotypes. These data show that chromosome number and structure exhibit a great deal of variation within the genus Begonia, and likely help to explain the large number of taxa found within the genus.

Chromosome studies in Hippeastrum (Amaryllidaceae): variation in genome size

This paper presents the karyotype and DNA content of 12 diploid species of Hippeastrum from South America. The variation in genome size is compared with the karyotype and DNA content of Amaryllis belladonna from South Africa. The Hippeastrum species present a uniform and bimodal basic karyotype formula, but significant differences are found in the total chromosome volume (TCV) and nuclear DNA content. A positive correlation between the DNA content and TCV is also observed. The karyotype’s constancy is a product of changes in DNA content occurring in the whole chromosome complement. The DNA addition to the long and short sets of chromosomes varies independently. In species with higher DNA contents, the short chromosomes add equal DNA amounts to both arms, maintaining their metacentric morphology, whereas the long chromosomes add DNA only to the short arm, increasing the chromosome symmetry. These data show that the evolutionary changes in DNA amount are proportional to chromosome length, maintaining the karyotypic uniformity. A. belladonna has a larger DNA content and possesses a karyotype different from that of Hippeastrum spp., supporting the distinction between the two genera and upholding the name Amaryllis for the South African entity against Hippeastrum for the South American genus. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155, 171–178.

Karyotype analyses and studies on the nuclear DNA content in 30 genotypes of potato (Solanum tuberosum) L.

The cytophotometric estimation of 4C DNA content, and karyotypic and somatic chromosome number analyses were carried out in 30 genotypes comprising seven cultivars and 23 advanced breeding lines of Solanum tuberosum. Detailed karyotype analysis revealed genotype specific chromosomal characteristics and structural alterations in chromosomes of the genome, with a rare phenomenon of aneusomatic (2n = 4x + 2 = 50) condition in cv.K. Chandramukhi. The origin of this variation could be attributed to mitotic non-disjunction in the shoots giving rise to aneusomatic roots. Highly significant variations in the genome length, volume and total form percentage were noted at the cultivar level. The total chromosome length varied from 84.56 microm in cv.K. Pukhraj to 127.62 microm in MS/89-60, with an average value of 100.94 microm +/- 1.82. Total chromosome volume varied from 57.22 microm3 in MS/92-1090 to 132.64 microm3 in JW-160. Significant variations in the 4C DNA content (7.28-15.83 pg) were recorded at the cultivar level, with an exceptionally high DNA content (22.24 pg) in cv.K. Chandramukhi. This could be due to the aneusomatic condition of this genotype. Correlation studies revealed interdependence between the chromosomal and nuclear parameters of the genotypes. Structural alterations in the chromosomes, as well as loss or addition of highly repetitive sequences in the genome, caused variations in DNA content at the cultivar level. Variations in genomic structure and nuclear DNA content of the 48-chromosome genotypes suggest a genetic drift during microevolution, leading to the development of new cultivars.

Variation of 4C DNA Content and Karyotype in Nine Cultivars of Fenugreek (Trigonella foenum-graecum L.)

ABSTRACT In situ nuclear DNA content estimations, karyotype analysis, and somatic chromosome number (2n = 16) were made for nine cultivars of fenugreek (Trigonella foenum-graecum L.), revealing cultivar specific chromosomal characteristics and minute structural alterations in chromosomes of the genome. The 4C DNA content varied significantly from 3.12 to 4.36 picograms. Significant variations were also observed in total chromosome length, total chromosome volume, and total form percentage at the cultivar level. Correlation coefficients showed interdependence between the chromosome length and chromosome volume within at the cultivar level. Variations in genomic structure and the nuclear DNA content of fenugreek cultivars, despite the same somatic chromosome number, suggest a genetic drift among the cultivars.

Cytophotometric Estimation of 4C DNA Content and Chromosome Analysis in Four Species of Astrophytum Lem. of the Family Cactaceae.

Karyotype analysis including determination of somatic chromosome number, chromosome length and volume, 4C DNA content and Interphase Chromosome Volume (INV) were carried out in Astrophytum asterias, A. capricorne, A. myriostigma var. nudum and A. ornatum of the family Cactaceae. Somatic chromosome number was 2n=22 in each of the studied species. Karyotype analysis showed minute structural alterations in the chromosomes. Total chromosome length varied from 56.65 μM in A. myriostigma cv. nudum to 60.76 μM in A. ornatum and the chromosome volume ranged from 48.12 pM3 in A. ornatum to 66.95 μM3 in A. myriostigma var. nudum. Significant changes on the TF% suggested the formation of the median chromosomes from the sub-median types in A. asterias and A. myriostigma var. nudum that might be due to translocation of chromosomes during evolution. Significant variations in the 4C DNA content were noticed among the species which ranged from 9.23 pg in A. capricorne to 10.12 pg in A. myriostigma var. nudum. Total chromosome volume and INV showed high degree of correlation with the nuclear DNA content of the species. Interspecific variability of the nuclear DNA content might be due to the variations in the repetitive DNA sequences of the genome. The structural alterations in the chromosomes as well as loss or addition of highly repetitive sequences in the genome caused variations in the nuclear DNA at interspecific level indicating a micro-change of nuclear material during evolution.

Karyotype, DNA Content and Meiotic Behaviour in Five South American Species ofVicia(Fabaceae)

This paper presents the karyotype, DNA content and meiotic behaviour of five species ofViciafrom Argentina (V. macrogramineaBurk.,V. gramineaSM.,V. epetiolarisBurk.,V. pampicolaBurk. andV. nanaVog.). All the species have the same chromosome number and karyotype formula (2n=14; 6m+4st+4t). Each species, however, displays a characteristic number and position of the nucleolar organizer region (NOR) and different sizes of the respective satellites, confirmed by Ag-NOR banding. Moreover, significant differences were found in the total chromosome volume (TCV) and DNA content of the species. Positive correlations between DNA content and TCV, and between DNA content and type of life cycle were also found. TCV and DNA content are lower inV. nana(annual) and higher inV. macrograminea(biennial–perennial). The material displayed marked karyotypic orthoselection, with similar karyotypes in all studied species, even when the overall chromosome size varied. Evolutionary changes in DNA amount are proportional to the relative length of each chromosome arm, maintaining karyotypic uniformity. Significant differences were found between the meiotic behaviour ofV. gramineaand that of the other species.V. gramineahas a lower frequency of ring bivalents and chiasmata per cell, and also has a lower interstitial chiasma frequency. In general, the results are congruent with the morphological data reported for these species.

Meiotic chromosome pairing in maize is associated with a novel chromatin organization

Three-dimensional light microscopy and the excellent cytological features of maize meiotic chromosomes are used to analyze the early events of chromosome synapsis. We demonstrate that the chromosomes undergo a dramatic structural reorganization prior to synapsis in zygotene. The unique features of prezygotene chromosomes are a partial separation of sister chromatids, an elongation of knob heterochromatin, an increase in surface complexity, a 50% increase in total chromosome volume, and a peripheral localization and alignment of telomeric, but not proximal, loci. At zygotene, chromosome volume decreases and chromosomes appear as single fibers. The specialized prezygotene chromosome morphology may facilitate homology recognition once the homologs have been brought together.

Karyotype, Nuclear and Chromosomal DNA Variation in Lens culinaris Med.

Detailed somatic karyotype analysis and nuclear DNA estimations in 10 varieties of lentil (Lens culinaris Med.) revealed significant intervarietal variation for chromatin and nuclear DNA contents. The lentil karyotypes were symmetric with preponderance of metacentric chromosomes. Secondary constrictions, located very near to centromere, were observed in one pair of chromosomes each in only 2 varieties, while in the remaining varieties they were not detectable. Correlation analysis revealed a positive linear relationship of 2C DNA amount with total chromosome volume and nuclear area while DNA density has negative relationship with nuclear area. The results indicate that quantitative DNA changes associated with evolution of varieties have affected all chromosomes within the complements but not to the same magnitude.

Chromosome weights and measures in Petunia

The 2C nuclear DNA amounts in diploid Petunia species are low, ranging from 1·73 to 3·00 picograms. The nuclear dry mass and the total chromosome volume are closely correlated with the nuclear DNA amount. So also is cell size measured in pollen grains. Increase in the total nuclear DNA within the genus is achieved by the addition of equal increments of DNA to all members of the chromosome complement irrespective of their size. It is suggested that the correlations and distribution patterns of DNA changes displayed by the natural species may serve as standards for monitoring and interpreting changes in genetic material which are associated with regeneration from protoplasts and callus.

Nuclear DNA variation among acridid grasshoppers

The nuclear DNA amount varies threefold among species of acridid grass­ hoppers. DNA amount is correlated with the total chromosome volume, as measured at metaphase of mitosis. Despite the large-scale variation in DNA amount and in the total volume of chromosome material there is a striking uniformity in respect of the relative sizes of chromosomes within complements. Males from the northern race ofCryptobothrus chrysophoruscontain about 20% more nuclear DNA than males from the southern race. The DNA difference may be explained by supernumerary segments within chromosomes in the northern populations. The magnitude of the DNA variation between these races is indicative of substantial genetic divergence. It may well be that the two races merit separate specific ranking.

Quantitative karyology of some species ofLuzula

The dimensions of metaphase chromosomes and nuclear DNA contents were measured in eight species ofLuzula. The 2 C DNA contents ranged from 8.51 pg inL. purpurea to 0.55 pg inL. pilosa. Total chromosome volume shows a linear relationship with DNA content; however, the total chromosome length of the complement of the different species is approximately constant. Nucleolar volume and the number of chromocentres in the different species also show a relationship with DNA content. Taken together, these data suggest that while chromosome fragmentation could have generated the present-day range of chromosome numbers in the genus, there have also been changes in the total quantity of DNA with the result that species with similar chromosome numbers have different DNA contents. The relationships of DNA content with chromosome volume inLuzula and other genera are compared and the differences discussed.