Variation In Chromosome Length Research Articles

A comparative karyological study of Helianthemum (Cistaceae): karyotype size, karyotype symmetry and evolution of chromosome number

In this study we assessed karyotype size and symmetry for a comprehensive taxonomic and geographic representation of Helianthemum and reconstructed chromosome number evolution in the genus. Using root tips, we photographed mitotic metaphase spreads to obtain chromosome number, total haploid (monoploid) length of the chromosome set (THL), karyotype formula, Stebbins’ classification of karyotype asymmetry, interchromosomal coefficient of variation of chromosome length (CVCL) and intrachromosomal mean centromeric asymmetry (MCA) using MATO (Measurement and Analysis Tools). We found that shifts in chromosome number are not a major driver in the evolution of Helianthemum, whose chromosome number evolved at a constant rate of single chromosome gain or loss. Karyotype asymmetry is very low and little variable in all taxonomic categories studied, with a predominance of metacentric and submetacentric small to medium-sized chromosomes about 3 μm at the genus level. However, total karyotype length varies from 16.91 μm to 47.84 μm at the species level, with a cytogenetic signature that is not conserved within subgenera and most sections. Overall, H. subg. Plectolobum shows both the longest and the most symmetrical karyotypes. We hypothesize that the variation in karyotype size in Helianthemum is likely a consequence of chromosome rearrangements that have occurred under selective pressures.

A Karyological Study of Tenualosa Ilisha (Hamilton, 1822) From the Confluence of Padma and Meghna River of Bangladesh

Tenualosa ilisha (Hamilton, 1822), commonly known as Hilsha shad is a valuable and highly acceptable species in terms of their high flavored properties. Hilsha shad has striking morpho-genetical adaptation to heterogeneous habitats across their migratory routes. Cytogenetic analysis demonstrates the changes in chromosomes. But none was focused on the cytogenetic analysis of T. ilisha in Bangladesh. T. ilisha was found to possess 2n = 42 number of chromosomes along with a karyotype formula: 1M + 31m + 8sm + 2st using giemsa staining technique. The results demonstrated ‘diffuse type of interphase nuclei, co-existence of continuous type and interstitial type of prophase chromosomes respectively. No heteromorphic sex chromosomes were determined cytologically. The presence of diverse types of chromosomes based on centromeric position, gradual decrease in total haploid chromosome complement, mean centromeric asymmetry, coefficient of variation of chromosome length and Stebbins’s classification highlighted its asymmetry in karyotype with advance nature. Therefore, the elemental karyological data will offer information for the proper identification, cytotaxonomical classification, expanding productivity and preservation of genetic resources ofT. ilisha. Bangladesh J. Zool. 49 (2): 243-255, 2021

Karyotypes and genome size of Adonis amurensis and Adonis apennina (Ranunculaceae) from Asian Russia

The karyotypes of Adonis amurensis from Amur Oblast,' and Adonis apennina from Altai Republic, Khakassia Republic, and Irkutsk Oblast' have been investigated. The karyotype formula was obtained as 2n = 2x =16 = 8m + 8sm(4sat) for all specimens. We estimated karyotype asymmetry through the calculation of the Coefficient of Variation of Chromosome Length (CVCL), Coefficient of Variation of Centromeric Index (CVCI), and Mean Centromeric Asymmetry (MCA), and determination of Stebbins asymmetry index. The chromosome set of Adonis amurensis was found to be more symmetrical than the chromosome set of Adonis apennina. The average absolute nuclear DNA content (2C–value) was originally determined for Adonis amurensis and Adonis apennina by flow cytometry and attained on average 20.38 pg and 17.29 pg, respectively.

Chromosome diversity and karyotype asymmetry analysis in four cultivated triploid and three diploid wild genotypes of Musa from North-East India

Ploidy and karyotype asymmetry of four cultivated Musa acuminata var. Luwaobi, var. Masung Tabi, var. Gopi and var. Poitrish Kola (2n = 3x = 33) and three wild seeded M. acuminata var. Ram Kola, Musa balbisiana var. Blung Thali and Musa laterita (2n = 2x = 22) were reported for the first time from North East India. The predominance of median constricted chromosomes was found as compared to sub-median constricted chromosome in all genotypes. The average chromosome length varied from 1.55 μm in var. Luwaobi to 1.92 μm in var. Ram Kola. Symmetric karyotype was recorded in the wild as compared to the cultivated Musa genotypes. Out of the twelve inter- and intra-chromosomal asymmetry indices studied, intra-chromosomal asymmetry index (A1) versus inter-chromosomal asymmetry index (A2), relative variation in the centromeric index (CVCI) versus relative variation in chromosome length (CVCL) and heterogeneity of chromosome length (AI) versus dispersion index were found most reliable to assess chromosome asymmetry. Most symmetric karyotype was found in var. Poitrish Kola of Tripura and most asymmetric karyotype was found in var. Luwaobi of Manipur among cultivated genotypes. Genotype var. Ram Kola showed more karyotype asymmetry among the wild Musa as compared to var. Blung Thali of Tripura and M. laterita of Sikkim. Phylogenetic tree obtained from chromosome characters revealed that var. Ram Kola has ancestral karyotype and was found to be distantly related from the others. Two wild seeded genotypes M. balbisiana var. Blung Thali and M. laterita were found to have close relationship with AB genome suggesting the phylogenetic ancestry with AA or AAA genotypes.

The highly rearranged karyotype of the hangingfly Bittacus sinicus (Mecoptera, Bittacidae): the lowest chromosome number in the order.

Cytogenetic features of the hangingfly Bittacus sinicus Issiki, 1931 were investigated for the first time using C-banding and DAPI (4',6-diamidino-2-phenylindole) staining. The karyotype analyses show that the male B. sinicus possesses the lowest chromosome number (2n = 15) ever observed in Mecoptera, and an almost symmetric karyotype with MCA (Mean Centromeric Asymmetry) of 12.55 and CVCL (Coefficient of Variation of Chromosome Length) of 19.78. The chromosomes are either metacentric or submetacentric with their sizes decreasing gradually. Both the C-banding and DAPI+ patterns detect intermediate heterochromatin on the pachytene bivalents of B. sinicus, definitely different from the heterochromatic segment at one bivalent terminal of other bittacids studied previously. The male meiosis of B. sinicus is chiasmate with two chiasmata in metacentric bivalents and one in the submetacentric bivalent. The sex determination mechanism is X0(♂), which is likely plesiomorphic in Bittacidae. Two alternative scenarios of karyotype origin and evolution in Bittacus Latreille, 1805 are discussed.

A study on genetic relationship between Allium sativum L. and Scadoxus multiflorus (Martyn) Raf. of Amaryllidaceae

The present investigation has been focussed on the inter-chromosomal and intra-chromosomal asymmetry data of Allium sativum and Scadoxus multiflorus of Amaryllidaceae using quali-quantitative and quantitative methods. The quail-quantitative analysis is strictly ratio based and it revealed that the karyotype of A. sativum and S. multiflorus belonged to category 1A and 3C respectively indicating only the degree of asymmetry. The coefficient of variation of chromosome length (CVCL) and the mean centromeric asymmetry (MCA) were the estimators of quantitative analysis and the data showed that the inter- and intra-chromosomal asymmetry were comparatively high in S. multiflorus than that of A. sativum. Further, the genetic distance between these two species is clearly visible in the bi-dimensional scattered plot from the derived MCA and CVCL data.

Karyomorphology and DNA quantification in the marine angiosperm Halophila stipulacea (Forsskål) Ascherson from Mediterranean and Red Seas

Cytogenetic studies for systematic and evolutionary purposes are lacking on marine phanerogams. Halophila stipulacea is a tropical seagrass that invaded the Mediterranean from the Red Sea through the Suez Canal. In this study, we report, for the first time, the karyotype features and genome size of H. stipulacea populations from different localities. Also, an attempt to compare our data with those reported in literature on other Halophila species is discussed. To determine the karyological relationships among taxa, we used basic karyotypic features such as chromosome number, size and symmetry, and position of chromosomal landmarks. To estimate karyotype asymmetry, the Coefficient of Variation of Chromosome Length (CVCL) and the Mean Centromeric Asymmetry (MCA) values were calculated. The estimations of DNA amounts were carried out by Image Cytometry (IC) using the interphase-peak method. All the taxa, including those reported in literature, present a uniform and slightly bimodal karyotype, but significant differences are found in nuclear DNA content among species. Each taxa had a karyotype formula 2n = 18 = 10m + 2sm + 6st. Aneuploidy and polyploidy seemed to not be involved in the speciation of this genus. The conserved karyotype in these taxa suggests the presence of mechanisms selecting for constancy, or against changes, in karyotype number and morphology.

Seed Morphology, Leaf Anatomy and Karyotype Analysis of the medicinal and ornamental plant; Vaccaria hispanica (Miller) Rauschert

Vaccaria hispanica (Miller) Rauschert is a monotypic genus which is in the family Caryophyllaceae. The plant is known as ‘‘Ekinebesi’’ in Turkey. It has been recorded in pharmacopoeias and also it has been cultivated as ornamental plant in Canada. The leaf anatomy V. hispanica has been determined, seed and chromosome morphology have been confirmed in this study. Somatic chromosome number has been determined as 2n=30. Relative variation in chromosome length and mean centromeric asymmetry of the species has been estimated. The examined species has bifacial and amphistomatic leaf. The lower stomatal index was estimated at 27.14%, the upper stomatal index was estimated as 13.20%.

Genome Size Diversity in Lilium (Liliaceae) Is Correlated with Karyotype and Environmental Traits.

Genome size (GS) diversity is of fundamental biological importance. The occurrence of giant genomes in angiosperms is restricted to just a few lineages in the analyzed genome size of plant species so far. It is still an open question whether GS diversity is shaped by neutral or natural selection. The genus Lilium, with giant genomes, is phylogenetically and horticulturally important and is distributed throughout the northern hemisphere. GS diversity in Lilium and the underlying evolutionary mechanisms are poorly understood. We performed a comprehensive study involving phylogenetically independent analysis on 71 species to explore the diversity and evolution of GS and its correlation with karyological and environmental traits within Lilium (including Nomocharis). The strong phylogenetic signal detected for GS in the genus provides evidence consistent with that the repetitive DNA may be the primary contributors to the GS diversity, while the significant positive relationships detected between GS and the haploid chromosome length (HCL) provide insights into patterns of genome evolution. The relationships between GS and karyotypes indicate that ancestral karyotypes of Lilium are likely to have exhibited small genomes, low diversity in centromeric index (CVCI) values and relatively high relative variation in chromosome length (CVCL) values. Significant relationships identified between GS and annual temperature and between GS and annual precipitation suggest that adaptation to habitat strongly influences GS diversity. We conclude that GS in Lilium is shaped by both neutral (genetic drift) and adaptive evolution. These findings will have important consequences for understanding the evolution of giant plant genomes, and exploring the role of repetitive DNA fraction and chromosome changes in a plant group with large genomes and conservation of chromosome number.

A New Cytotype of the Iranian House Mouse, Mus musculus Linnaeus, 1758 (Rodentia: Muridae), in Birjand Region, Eastern Iran: Implications for the Evolution of Sex-Autosome Translocations

The highly conserved morphology and chromosomal structures of house mouse, Mus musculus, provides a good model for chromosomal studies. Sex-autosome translocations is one of the rarest chromosomal rearrangements among mammals and therefore sex-autosome translocations has been offered as accurate taxonomic markers to identify species with similar morphological traits. In this study, we described the outcome of a comprehensive cytogenetic survey of the house mouse, Mus musculus, in the eastern Iran using G banding method. Interestingly, results showed the presence of a new cytotype of X-autosome translocation of house mouse which was found in 18 specimens of Birjand region in the eastern Iran. Larger size of choromosomal translocation was observed in Chromosome X. We used karyotype asymmetry method as a powerful statistical parameter to extract coefficient of variation of chromosome length. Based on the data of this study, the results, Birjand population did not show asymmetry in all Asymmetry indexes (AI, DI, As%, A, A2, A1 and Syi%), and this result confirmed translocations in Birjands' chromosomes as well.

Karyotype analysis of Minuartia mesogitana subsp. mesogitana and Minuartia elmalia (Caryophyllaceae, Alsinoideae).

Mitotic metaphase chromosomes, karyotypic characters, monoploid karyograms and ideograms of Minuartia mesogitana subsp. mesogitana and Minuartia elmalia were investigated. Analysis of somatic metaphases showed that the chromosome numbers and the karyotype formula of these taxa were 2n = 2x = 24 = 8m + 8sm + 8st for Minuartia mesogitana subsp. mesogitana and 2n = 2x = 32 = 12m + 16sm + 4st for Minuartia elmalia. No satellites were observed in the karyotypes of the taxa. The intrachromosomal and interchromosomal karyotype asymmetries were estimated with Mean Centromeric Asymmetry (MCA) and Coefficient of Variation of Chromosome Length (CVCL).

Karyotype analysis of four species of Dianthus section Fimbriati (Caryophyllaceae, Sileneae)

AbstractKaryotypic characters, mitotic metaphase chromosomes, monoploid ideograms and karyograms of Dianthus L. section Fimbriati Boiss., D. tabrisianus Bien.ex Boiss., D. sessiliflorus Boiss., D. stramineus Boiss. & Heldr., and D. erythrocoleus Boiss. were investigated for the first time. Analysis of somatic metaphases showed that the chromosome numbers and the karyotype formula of these taxa were 2n = 30 = 22m + 6sm + 2st for D. tabrisianus, 2n = 30 = 14m + 8sm + 8st for D. sessiliflorus, 2n = 30 = 20m + 4sm + 6st for D. stramineus and 2n = 30 = 18m + 8sm + 4st D. erythrocoleus. No satellites were observed in the karyotypes of these species. The interchromosomal and intrachromosomal karyotype asymmetries were estimated with coefficient of variation of chromosome length (CVCL) and mean centromeric asymmetry (MCA).

Karyotype analysis in someCharaspecies (Charales, Charophyceae) in Iran

AbstractKaryological characteristics were determined in 36 populations of eight Chara species and varieties distributed in Iran. The karyotype asymmetry/symmetry were evaluated using CVCL (coefficient of variation of chromosome length), CVCI (heterogeneity of the centromeric index) and MCA (mean centromeric asymmetry). Results obtained from the current study revealed that there are two different ploidy levels (n = 14 and n = 28) among the investigated taxa. All eight species and varieties had metacentric (M & m), sub-metacentric (Sm) and sub-telocentric (St) chromosomes, but the majority of taxa showed a dominance of metacentric and sub-metacentric chromosomes. In general, the karyotypes within the genus Chara were symmetrical, but the studied species differed significantly in quantitative features of karyotype and revealed the occurrence of qualitative changes during the species diversification. The present study reveals that karyological features may be of great help in Chara species delimitations.

Cytotaxonomy of some species ofVernonanthuraandVernonia(Asteraceae, Vernonieae) from South America

AbstractThe number and behavior of meiotic chromosomes in four populations of three species of Vernonanthura were analyzed. It was observed that all stages of meiosis were stable without chromosomal irregularities. The somatic chromosome number is reported for four populations of three species of Vernonanthura and two populations of Vernonia. All species were diploid with 2n = 34. The first chromosome count is presented for Vernonanthura chaquensis (2n = 17II and 2n = 34). The karyotypes were determined for Vernonanthura lucida (32m + 2sm), V. oligactoides (24m + 10sm) and V. pseudolinearifolia (28m + 6sm); they are presented for the first time. The total length of the karyotype was 31.67μ–40.48 μm. The average chromosome length was 1.86μ–2.38 μm and the centromeric index was 38.61–42.99. Vernonanthura oligactoides showed the smallest variation of chromosome length within the karyotype (1.42 μm) while V. squamulosa had the biggest (2.15 μm). The different karyotypic parameters were analyzed with two stati...

Karyotype analysis of theCalligonum mongolicumcomplex (Polygonaceae) from Northwest China

This study focused on the karyotype characters, mitotic metaphase chromosomes, monoploid idiograms and karyograms of the Calligonum mongolicum Turcz. (Polygonaceae) complex which includes Calligonum chinense A. Los., Calligonum gobicum A. Los., Calligonum pumilum A. Los., and Calligonum zaidamense A. Los., which were investigated for the first time. Analysis of somatic metaphases showed that the chromosome numbers and the formulae of the taxa were 2n = 2x = 18 = 8m + 10sm and 2n = 3x = 27 = 8m + 8sm + 2st for C. mongolicum in Qingtongxia, Ninxia Erlianhot, Inner Mongolia; 2n = 2x = 18 = 8m + 8sm + 2st for C. mongolicum in Erjina, Inner Mongolia;, 2n = 2x = 18 = 6m + 12sm for C. mongolicum in Yumen, Gansu; 2n = 2x = 18 = 8m + 8sm + 2st for C. chinense in Zhangye, Gansu; 2n = 2x = 18 = 6m + 12sm for C. gobicum in Ejina, Inner Mongolia; 2n = 2x = 18 = 4m + 14sm for C. pumilum in Hami, Xinjiang; and 2n = 2x = 18 = 10m + 8sm for C. zaidamense in Zhangye, Gansu. No satellites were observed in the karyotypes of these taxa. Karyotype asymmetry was estimated by Stebbins classification, karyotype asymmetry index (As.K %), total form per cent (TF %), Rec and Syi indices, intrachromosomal asymmetry index (A1) and interchromosomal asymmetry index (A2), dispersion index (DI), degree of asymmetry of karyotype (A index), asymmetry index (AI), coefficient of variation of centromeric index (CVCI), mean centromeric asymmetry (MCA), and coefficient of variation of chromosome length (CVCL).

A proposal for a multivariate quantitative approach to infer karyological relationships among taxa

Until now, basic karyological parameters have been used in different ways by researchers to infer karyological relationships among organisms. In the present study, we propose a standardized approach to this aim, integrating six different, not redundant, parameters in a multivariate PCoA analysis. These parameters are chromosome number, basic chromosome number, total haploid chromosome length, MCA (Mean Centromeric Asymmetry), CVCL (Coefficient of Variation of Chromosome Length) and CVCI (Coefficient of Variation of Centromeric Index). The method is exemplified with the application to several plant taxa, and its significance and limits are discussed in the light of current phylogenetic knowledge of these groups.

Karyological analysis of bitter gourd (Momordica charantia L., Cucurbitaceae) from Southeast Asian countries

Momordica charantia L. (Cucurbitaceae) is a commonly cultivated functional food plant. In the present study, karyological variation among 34 accessions of M. charantia originating from the Indian subcontinent (Bangladesh, India and Pakistan) and Thailand was evaluated. Ploidy levels ranging from diploid (2n= 22) to hexaploid (2n= 66) were observed. Hexaploidy in M. charantia is reported herein for the first time. Chromosome length ranged from 0.8 to 2.9 μm. The hexaploid accessions had submetacentric and subtelocentric chromosomes. All accessions harboured median and submedian chromosomes. Only one hexaploid accession (TOT1140) had chromosomes with subterminal centromeres. There was considerable variation in chromosome length and chromosome arm ratio.

Breakage-fusion-bridge Cycles and Large Insertions Contribute to the Rapid Evolution of Accessory Chromosomes in a Fungal Pathogen

Chromosomal rearrangements are a major driver of eukaryotic genome evolution, affecting speciation, pathogenicity and cancer progression. Changes in chromosome structure are often initiated by mis-repair of double-strand breaks in the DNA. Mis-repair is particularly likely when telomeres are lost or when dispersed repeats misalign during crossing-over. Fungi carry highly polymorphic chromosomal complements showing substantial variation in chromosome length and number. The mechanisms driving chromosome polymorphism in fungi are poorly understood. We aimed to identify mechanisms of chromosomal rearrangements in the fungal wheat pathogen Zymoseptoria tritici. We combined population genomic resequencing and chromosomal segment PCR assays with electrophoretic karyotyping and resequencing of parents and offspring from experimental crosses to show that this pathogen harbors a highly diverse complement of accessory chromosomes that exhibits strong global geographic differentiation in numbers and lengths of chromosomes. Homologous chromosomes carried highly differentiated gene contents due to numerous insertions and deletions. The largest accessory chromosome recently doubled in length through insertions totaling 380 kb. Based on comparative genomics, we identified the precise breakpoint locations of these insertions. Nondisjunction during meiosis led to chromosome losses in progeny of three different crosses. We showed that a new accessory chromosome emerged in two viable offspring through a fusion between sister chromatids. Such chromosome fusion is likely to initiate a breakage-fusion-bridge (BFB) cycle that can rapidly degenerate chromosomal structure. We suggest that the accessory chromosomes of Z. tritici originated mainly from ancient core chromosomes through a degeneration process that included BFB cycles, nondisjunction and mutational decay of duplicated sequences. The rapidly evolving accessory chromosome complement may serve as a cradle for adaptive evolution in this and other fungal pathogens.

Karyotype asymmetry: again, how to measure and what to measure?

One of the most popular, cheap and widely used approaches in comparative cytogenetics – especially by botanists – is that concerning intrachromosomal and interchromosomal karyotype asymmetry. Currently, there is no clear indication of which method, among the many different ones reported in literature, is the most adequate to infer karyotype asymmetry (especially intrachromosomal), above all in view of the criticisms recently moved to the most recent proposal published. This work addresses a critical review of the methods so far proposed for estimation of karyotype asymmetry, using both artificial and real chromosome datasets. It is shown once again how the concept karyotype of asymmetry is composed by two kinds of estimation: interchromosomal and intrachromosomal asymmetries. For the first one, the use of Coefficient of Variation of Chromosome Length, a powerful statistical parameter, is here confirmed. For the second one, the most appropriate parameter is the new Mean Centromeric Asymmetry, where Centromeric Asymmetry for each chromosome in a complement is easily obtained by calculating the difference of relative lengths of long arm and short arm. The Coefficient of Variation of Centromeric Index, strongly criticized in recent literature, is an additional karyological parameter, not properly connected with karyotype asymmetry. This shows definitively what and how to measure to correctly infer karyotype asymmetry, by proposing to couple two already known parameters in a new way. Hopefully, it will be the basic future reference for all those scientists dealing with cytotaxonomy.

A karyological study of some Dianthus L. species (Caryophyllaceae) in Northeast of Iran

AbstractThis study focuses on karyological investigation of four taxa of Dianthus (Caryophyllaceae) including D. crossopetalus, D. orientalis subsp. stenocalyx, D. orientalis subsp. gorganicus, and Dianthus sp. distributed in Northeast of Iran. The karyotype asymmetry/symmetry was evaluated using two methods: 1) CVCL (coefficient of variation of chromosome length) and CVCI (heterogeneity of the centromeric index); and 2) MCA (mean centromeric asymmetry). The karyotype asymmetry was also used to investigate the relationships among the taxa. Results obtained from the current study revealed that there are two different ploidy levels (2n = 2x = 30 and 2n = 4x = 60) among the investigated taxa. The indices CVCL and MCA described karyotype asymmetry correctly based on variation in chromosome length. Diagram of CVCL vs. MCA seems to be appropriate for karyological delimitation and taxonomic relationships among the Dianthus taxa under study. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)