Median Centromeres Research Articles

Cytopalynological studies in some Convolvulaceae members from northern Western Ghats, India

ABSTRACTThis paper presents a cyto-palynological study of four species of Convolvulaceae from the northern Western Ghats of India. Ipomoea clarkei and Operculina tansaensis are endemic to the region, whereas I. diversifolia and O. turpethum show wide distribution. A new cytotype with 2n = 28 was reported for I. diversifolia. The chromosome number 2n = 30 in O. turpethum was in conformity with earlier reports. Chromosome numbers for I. clarkei and O. tansaensis (both with 2n = 30) were reported for the first time. Meiosis was found to be normal. At diakinesis 14 bivalents were observed for I. diversifolia while I. clarkei and O. tansaensis showed 15 bivalents. In all the species, chromosomes were small with median region centromeres. The largest chromosome was recorded in I. clarkei (2.15 ± 0.25 µm) and the shortest for I. diversifolia (1.62 ± 0.19 µm). The karyotypes were symmetrical and exhibited Stebbins’s 4a category. Pollens were pantoporate-echinate in both the Ipomoea species and tricolpate-smooth i...

Cytopalynological studies in Zanonia indica (Cucurbitaceae), a monotypic genus

This paper presents first cytogenetical analysis of a monotypic genus, Zanonia indica (Cucurbitaceae). The diploid chromosome number was 2n = 2x = 30. Male meiosis was normal and revealed 15 bivalents at diakinesis. Karyotype was symmetrical (Stebbins’s 4a category). All chromosomes possessed median centromere. Chromosome length ranged from 1.10 ± 0.14 µm to 1.98 ± 0.33 µm. Mean chromosome length (MCL) was 1.47 ± 0.24 µm. Pollen grains were tricolporate and prolate with P/E ratio 1.49.

Cytological Investigation of Brazilian Nightshade (<i>Solanum seaforthianam</i> Andr.)

Solanum genus namely Solanum seaforthianum Andr. belongs to the Solanaceae family, and comprises only dioeciously species. These plants are distributed between 29º and 40º south. All species of this genus are diploid with chromosome numbers of 2n = 24, 28 and 30. According to literature, the basic chromosome number in this genus is x = 12, 14 and 15. Solanum genus with a chromosome complement of 2n = 30 has a symmetric karyotype with a median and sub median centromere position. Because ancestral species have a symmetric karyotype, it seems that x = 12 is the initial basic chromosome number in this genus and the x = 14 and x = 15 derived from x = 12. So it seems that diploid phenomena played an important role in evolution and speciation

Cytological Investigation of Brazilian Nightshade (<i>Solanum seaforthianam</i> Andr.)

Solanum genus namely Solanum seaforthianum Andr. belongs to the Solanaceae family, and comprises only dioeciously species. These plants are distributed between 29º and 40º south. All species of this genus are diploid with chromosome numbers of 2n = 24, 28 and 30. According to literature, the basic chromosome number in this genus is x = 12, 14 and 15. Solanum genus with a chromosome complement of 2n = 30 has a symmetric karyotype with a median and sub median centromere position. Because ancestral species have a symmetric karyotype, it seems that x = 12 is the initial basic chromosome number in this genus and the x = 14 and x = 15 derived from x = 12. So it seems that diploid phenomena played an important role in evolution and speciation

Karyotype of the Baikal amphipod Polyacanthisca calceolata Bazikalova, 1937, (Crustacea, Amphipoda)

The karyotype of the endemic Baikal amphipod Polyacanthiska calceolata Bazikalova, 1937 was analysed for the first time. A diploid number (2n=52) and general chromosome morphology (with a median centromere) are typical amongst Gammaridea. A peculiar feature of the karyotype was its pronounced symmetry caused by the presence of metacentric (equal-armed) chromosomes insignificantly varying in size (from 5 to 8 μm). Sex chromosomes have not been distinguished. Supernumerary B chromosomes were regularly found in the metaphase plates of embryos P. calceolata, and may serve as an adaptive mechanism of this species to perform migrations to areas of gas hydrate seeps.

Karyological studies of some representatives of Tanacetum L. (Anthemideae-Asteraceae) from north-east Anatolia

The karyotypes of nine Tanacetum taxa distributed in north-east Anatolia, Turkey, were determined and evaluated by cluster analysis and principal-components analysis. Chromosome numbers were 2n = 2x = 18 (8 taxa) and 4x = 36 (1 taxon). Somatic chromosome numbers of two taxa and a new ploidy level in one taxon are reported for the first time. Karyotype analysis indicated that chromosomes of Tanacetum taxa have predominantly median centromeres. The taxa studied differed significantly in the size of the short arms and long arms, and the arm ratio of each pair of homologous chromosomes, indicating structural rearrangements of the chromosomes have been involved in diversification of the taxa. They were placed in 2A, 3A, and 2B of Stebbins’ karyotype classification, showing the presence of a primitive symmetrical karyotype in the genus. Several systematic and evolutionary aspects of the genus are discussed on the basis of karyological data.

Karyotype and meiotic analysis of five species in the genusArtemisia

Abstract The karyotypes and meiotic behaviour of five species in Artemisia are investigated. The results are concluded as following: A. absinthum Linn., A. sieversiana Ehrhart ex Willd. and A. annua Linn. are diploids; while A. abrotanum Linn. and A. japonica Thumb. are tetraploids. Their karyotypes consist mainly of median centromere and submedian centromere chromosomes, except that A. sieversiana, A. abrotanum and A. japonica have one, one and two pairs of subterminal centromere chromosomes. One pair of satellited chromosomes is respectively observed in A. annua, A. sieversiana and A. absinthum. All the species have a 2A type karyotype. The mean configurations per the pollen mother cells (PMCs) of A. absinthum, A. sieversiana and A. annua are 0.03I + 8.82II + 0.08IV, 1.16I + 8.26II + 0.03III + 0.06IV and 2.15I + 7.78II + 0.04III + 0.04IV; the mean configurations of A. abrotanum and A. japonica are 0.11I + 16.83II + 0.08III + 0.50IV and 0.17I + 16.67II + 0.07III + 0.57IV, respectively. The meiotic behaviour in the PMCs of all species is generally normal, however, higher frequencies of univalents are observed both in A. annua and A. sieversiana. A low frequency of quadrivalents (and trivalents) and chromosome bridges/lagging chromosomes is observed.

Multiple chromosome aberrations in a lymphosarcomatous tumor.

The chromosomes of a lymphoblastic sarcoma were investigated in 2 biopsies from the malignant lymph nodes. Both biopsies had the same highly stable stemline karyotype, analyzed both by the classical orcein technique, including tritium autoradiography and measurements of all chromosomes of 10 cells, and by the new fluorescence technique. In relation to the normal human karyotype, the stemline had undergone changes in the proportions of the normal chromosome types and had acquired several marker chromosomes. With the aid of fluorescence technique some of the marker chromosomes were identified as parts of normal chromosomes, whereas others were not recognized. The latter included 3 medium-sized metacentrics with completely median centromere and the same fluorescence pattern in both arms. They were similar in every respect to marker chromosomes recently found in 4 other malignant lymphomas. The possible significance of these findings is discussed.

Karyotype and meiotic analyses of six species in the subtribe Chrysantheminae

The karyotypes and meiotic behaviour of six Chrysantheminae species are investigated. Pyrethrum coccineum (Willd.) Worosch. is a tetraploid, while the other five species (Argyranthemum frutescens (L.) Sch.-Bip., Opisthopappus taihangensis (Ling) shih, Crossostephium chinense (L.) Makino, Tanacetum vulgare L. and P. parthenium (L.) Sm.) are all diploids. Their karyotypes consist mainly of median centromere and submedian centromere chromosomes, although C. chinense also has two terminal centromere chromosomes, and P. parthenium two subterminal centromere chromosomes. No satellited chromosomes are observed in any of the six species. All the species have a 2A type karyotype, except for P. coccineum which is 3A. The meiotic behaviour in the pollen mother cells (PMCs) of all six species is essentially normal, with metaphase I chromosome pairing configurations in the diploid species predominantly showing 9II, while P. coccineum shows 18II. A low frequency of quadrivalents (and trivalents) and chromosome bridges/lagging chromosomes is observed.

Chromosome number, karyotype morphology, heterochromatin distribution and nuclear DNA content of some talitroidean amphipods (Crustacea: Gammaridea)

Chromosome number, karyotype formula, C-banding pattern, genome size and DNA base composition were studied in three species of Hyalidae and seven species of Talitridae. A karyotype of 25 chromosome pairs, with median centromeres (FN = 100), was found in all the species of Talitridae analysed and Apohyale prevostii. Genome size (C-value) varies among Talitrida from 0.94 pg in Apohyale crassipes to 2.81 pg in Orchestia gammarellus, and the percentage of AT-DNA in the whole genome ranges from 56.12% in A. crassipes to 68.17% in Sardorchestia pelecaniformis. In comparison with Hyalidae, Talitridae show more uni- formity in chromosome number and karyotype formula, and have larger genomes. There is a direct correlation between total DNA content and the amount of C-heterochromatic DNA. The cytogenetical data on Talitrida were compared from a phylogenetic and an evolutional point of view. The increase in genome size during the evolution of the Talitrida possibly had a role in their adaptation to supralittoral life and extreme subaerial conditions.

Characterization of chromosomes and genome organization of Thapsia garganica L. by localizations of rRNA genes using fluorescent in situ hybridization.

The karyotype (2n = 22) of Thapsia garganica L. (Apiaceae, Apioideae, Laserpitieae) was constructed using molecular cytogenetics. The size of the 22 chromosomes ranged between 5 and 10 microns. Two chromosomes had satellites on the short arms. The 18S-5.8S-26S rDNA genes were located to the two satellites by fluorescent in situ hybridization (FISH). The 5S rDNA repeat unit was amplified and located by FISH to one pair of the non-satellited chromosomes. Sequencing 5S rDNA of T. garganica revealed two classes of genes based on distinct intergenic spacer regions of 191/193-bp and 181-bp. respectively. The ITS1 and ITS2 of the 18S-5.8S-26S repeats were also amplified and phylogenetic analysis placed T. garganica in a distinct clade from the Daucus clade containing Laserpitium sp. The organization of T. garganica L. genome is tentatively divided in group A of 14 chromosomes with median centromere and of which one pair (q/p 1.22) contains single 5S rDNA locus on the long arm. Group B consists of six chromosomes with subterminal centromeres (q/p between 4.23 and 7.92) and finally group C with the satellited chromosome pair containing the 18S-5.8S-26S rDNA locus at the secondary constriction.

The Fine Structure of Egyptian Henbane (Hyoscyamus muticus L.) Chromosomes as Revealed by Pachytene Analysis.

The morphology of the pachytene chromosomes of Hyoscyamus muticus (2n=28) was analysed. All 14 pachytene chromosomes were clearly identified on the basis of length, arm ratio, distribution of heterochromatin and presence of characteristic chromomeres. The pachytene chromosomes were differentiated into proximal heterochromatic regions surrounding the centromere and distal euchromatic regions. Chromosomes were numbered from 1 to 14 following a descending order of length. The physical lengths of the 14 chromosome pairs ranged from 28.23 to 101.47 μm with a total length of 877.69 μm. Based on the centromere position, the complement consisted of 4 chromosomes with median centromeres, 7 with subterminal centromeres and 3 with terminal centromeres.

Evolutionary Trend in Lens culinaris and Allied Spcies. A Cytological Evidence.

The karyotype of 20 cultivated varieties of lentil and 3 wild species revealed a good deal of structural variations. The chromosomal length ranged from 4.58 to 7.50 μm in L. orientalis, 3.86 to 6.11 μm in L. nigricans and 3.81 to 8.37 μm in L. montbrettii. The karyotype of L. montbrettii was assymetrical. Secondary constriction was noticed in the longest chromosome of the L. montbrettii and L. orientalis whereas it was present on the 3rd pair in L. nigricans. Total chromatin length. was 44.5 μm in L. orientalis, 34.64 μm in L. nigricans and 39.64 μm in L. montbrettii. Out of 20 genetic stocks of lentil most possessed 4-7 chromosomes with submedian centromere. In some varieties like L 3991, 74 TA 9/ILL 15 and LC 112, 3 to 4 pairs of chromosomes possessed median centromere. The size difference between the shortest and the longest chromosomes in most of the strains was less than 2 μm. Among different varieties “J” shape submetacentric chromosomes outnumbered the “V” shape metacentric chromosomes. Submetacentric chromosomes approaching acrocentric condition was found in few varieties like WYR 1811, 74 TA 276/ILL 262, 75 KT 36261/ILL 553 and Pant L 639. Most of the exotic lentil accessions possessed 0-1 metacentric and 6-7 submetacentric chromosomes and indigenous lines possessed 2-5 submetacentric and 2-4 metacentric chromosomes. Most of the karyotypes are symmetrical but a tendency towards evolution of asymmetrical is very much apparent within the species as also revealed by T. F. Meiosis in the majority of the cultivars under study showed near normal chromosomal pairing, except infrequent occurrence of univalents and multivalents. The average chiasmata frequency per bivalent was found to range from 0.8 to 1.8 in different cultivars. The exotic macrosperma cultivars in general possessed lesser chiasmata per bivalent indicating them as genetically advanced. The number of rod bivalents outnumbered the ring bivalents in all the wild species.

Karyotypes and evolutionary relations of Hibiscus asper Hook., H. cannabinus L. and H. surattensis L. (Malvaceae)

Studies were made of the morphology and karyotype of accessions of H. asper, H. cannabinus and H. surattensis. There were six simple epicalyx segments in H. asper, nine in H. cannabinus and ten branched and leafy epicalyx segments in H. surattensis. Karyotypic analysis of the species showed a preponderance of median centromeres. H. surattensis had a more symmetrical karyotype and smaller chromosomes than H. asper and H. cannabinus. H. asper had the longest chromosomes. Ten of their chromosomes were significantly different in length, while four were significantly different in arm ratio.

Karyomorphology of some Moraceae and Cecropiaceae (Urticales)

The karyomorphology of 16 species in 13 genera representing Moraceae and Cecropiaceae was investigated in an effort to contribute to a better understanding of chromosome features and evolution in the families. All genera investigated have similar karyomorphology, but differences are found in (1) chromosome features of Interphase nucleus (simple, simple-complex, or complex chromocenter type), (2) basic chromosome number (x=13 or 14), (3) size variation (mono-or bimodial), and (4) frequencies of chromosomes with median centromeres (m-chromosome) (25–85%) and those with subterminal (or terminal) centromeres (st-chromosome) (14–69%). Comparisons with Ulmaceae as an outgroup of the remainder of Urticales suggest that the simple chromocenter type,x=14 comprising bothm- andst-chromosomes, and the monomodial karyotype are plesiomorphies in Moraceae and Cecropiaceae. Most of Moraceae and Cecropiaceae retain generalized chromosome features of the order, but have involved a few evolutionary changes in karyomorphology. Based on some detailed karyomorphological data, inter- and infrafamilial relationships are also briefly discussed.

Mitotic and meiotic behaviour of B-chromosomes ofGuizotia scabra(Vis.) Chiov. ssp.scabra(Compositae)

SUMMARYGuizotia scabra ssp. scabra plants grown from seeds originating from southwest Ethiopia were found to carry 1–4 and 1–6 B-chromosomes in root tip cells and pollen mother cells, respectively. The B-chromosomes were of three morphological types, being large in size with a median or submedian centromere or smaller in size with a likely median centromere. They are all numerically stable within and between root tips, but in most of the plants their numbers in the pollen mother cells were higher than in the roots. When single, a B-chromosome remained as a univalent. When two or more were present, they paired with one another, most frequently as bivalents, with chiasmata in one or both arms. They had a high frequency of normal segregation at anaphase I and subsequent stages of meiosis. After application of C-banding technique, the large B-chromosomes with a median centromere did not show C-bands.

Karyotype analysis and optimization of mitotic index in Picea mariana (black spruce) preparations from seedling root tips and embryogenic cultures

The effect of hydroxyurea and colchicine solutions on mitotic index was investigated in embryogenic suspensions and in seedling root tips of Picea mariana. Hydroxyurea treatment and 0.6 per cent colchicine solution significantly increased the quantity of mitotic cells which were mostly in the metaphase stage. The highest mitotic index was observed in cells of embryogenic suspensions. The embryogenic lines were cytologically stable and their utilization for karyotype studies and technique development holds great potential. The arm ratios and relative chromosome length values showed the same trends between embryogenic cultures and seedling root tips and among the five black spruce populations studied. This study shows that the black spruce karyotype is asymmetric and semi-advanced, as in Larix and Abies. Three pairs of chromosomes are of the sm-type with submedian centromeres. One pair is median-submedian (msm), six pairs are m-type having median centromeres and two pairs are metacentric or M-type.

Structural heterozygosity inIris variegataL.

SUMMARYFour chromosomes in the karyotype of a clone of Iris variegata L. were heteromorphic. On the basis of somatic chromosome morphology and meiotic associations, it is established that the heteromorphicity is due to translocation involving shifting of a large segment of the long arm of the longest chromosome with nearly median centromere on the short arm of the smallest chromosome with submedian centromere, giving rise to two medium sized chromosome with nearly median and submedian centromeres. Bridge-fragment configurations at metaphase I also suggest the involvement of paracentric inversion heterozygosity. While the basic karyotype of I. variegata appears to be similar to that of the other species of bearded irises with 24 chromosomes, structural alterations, similar to the one presently recorded, have probably been responsible for the reported variations in its karyotype.

Karyomorphology and evolution in some Hamamelidaceae and Platanaceae (Hamamelididae; Hamamelidales)

Karyomorphology in 14 species of 12 genera representing a variation of Hamamelidaceae and in one species of Platanaceae (Platanus only) is investigated in an effort to contribute to an understanding of chromosome evolution and inter- and intrafamilial relationships. All genera investigated show similar chromosome features at resting stage and prophase, excepting that at resting stageRhodoleia shows the simple, rather than the simple-complex, chromocenter type as in other genera. At metaphase all the genera investigated of Hamamelidaceae, like other ‘lower’ Hamamelididae, have chromosomes with median centromeres (m-chromosomes), those with submedian centromeres (sm-chromosomes) and those with subterminal (or terminal) centromeres (st-t-chromosomes) at different frequencies, although frequencies ofst-t-chromosomes are always less than 33%. InPlatanus,m-chromosomes are lacking and insteadst-t-chromosomes are predominant (86%), a feature seemingly very specialized. We confirmedx=7 in Platanaceae,x=12 in Hamamelidoideae and Rhodoleioideae, andx=8 in Exbucklandioideae and Altingioideae (Hamamelidaceae). An analysis of chromosome morphology supports the hypothesis thatx=12 in the former two subfamilies is of tetraploid origin fromx=6, rather than of triploid origin fromx=8. We further give brief comments on the suprageneric classification of Hamamelidaceae that was recently proposed by Endress.

Karyomorphology and relationships of Celtidaceae and Ulmaceae (Urticales)

Based on karyomorphological features, six (examined in this study) of nine genera of Celtidaceae are divided into three groups: 1)Celtis, Parasponia, Pteroceltis andTrema; 2)Aphananthe; 3)Gironniera, and six genera of Ulmaceae into two: 1)Holoptelea andPhyllostylon; 2)Hemiptelea, Planera, Ulmus andZelkova. The first four genera share the simple chromocenter type at the resting stage andx-10, with all chromosomes with submedian or median centromeres (frequency of chromosomes with subterminal or terminal centromeres 0%, although uncertain inTrema).Aphananthe hasx=13, but resembles the above four genera in other features.Gironniera is distinct from all other Celtidaceae in having the diffuse-complex chromocenter type andx=14, features which occur in Ulmaceae. InGironniera the frequency of chromosomes with subterminal or terminal centromeres is 43%, a proportion similar to those inHoloptelea (36%) andPhyllostylon (58%) of Ulmaceae. All six genera of Ulmaceae havex=14, yetHemiptelea, Planera, Ulmus andZelkova are distinct fromHoloptelea andPhyllostylon (with the simple chromocenter type) in having the diffuse-complex chromocenter type and in predominantly possessing chromosomes with subterminal or terminal centromeres (93%). Evidence from karyomorphology, as well as from other sources, suggests 1) thatAphananthe (x=13) is most distantly related to all genera withx=10 within Celtidaceae, 2) thatGironniera may have a key role for understanding evolutionary relationships between Celtidaceae and Ulmaceae, and 3) thatHoloptelea andPhyllostylon represent derivatives of a line that diverged early from a common ancestor or all Ulmaceae. On the basis of comparisons with other Urticales and the putative outgroups of the order, it is also suggested that the chromosome morphology of Ulmaceae represents the more derived state in Urticales.