Mitotic Prophase Chromosomes Research Articles

Karyomorphological Studies in Some Species of Parnassia L. (Saxifragaceae s.l.) in East Asia and Intraspecific Polyploidy of P. palustris L.

Karyomorphological information is one of the most important characters for cytotaxonomy. We described karyomorphology of 14 species of Parnassia in East Asia. They had commonly the resting chromosomes of the simple chromocenter type and the mitotic prophase chromosomes of the proximal type. The somatic chromosome number of 2n=14 was shown in three species, that of 2n=18 was shown in six species, that of 2n=18 or 36 was shown in two species, that of 2n=32 was shown in one species, that of 2n=36 or 36+1∼8 s was shown in one species, and that of 2n=18, 27, 36 or 45 was shown in one species. They were commonly monomodal (gradual) decrease in length from the largest to the smallest chromosomes. However, their absolute chromosome sizes were different from each other. Average chromosome sizes were recognized as three types small (1.21 μm), medium (1.7–2.36 μm), and large (3.1–3.75 μm). Parnassia palustris showed four cytotypes that could be likely cytogeographically correlated with habitats, polyploidy, and sizes of pollen grains.

Karyotype Analysis of an Endemic Species Primulina tabacum (Gesneriaceae)

The cytology of an endemic species Primulina tabacum (Gesneriaceae) was studied in this paper. The chromosome numbers and karyotype were investigated for the first time. The results revealed that the interphase nuclei were categorized to be rod prochromosome type and the mitotic prophase chromosomes were classified as proximal type. The chromosome number was 2n=36. The karyotype formula was 2n=2x=36=24m (1SAT)+12sm and the karyotype is 2A type.

Cytogenetic study of three edible chrysanthemum cultivars

During past decades, edible chrysanthemum (Dendranthema x grandiflorum) has become a popular dietary supplement. However, only numberable cultivars are available, cytogenetic studies especially meiotic behaviour in them remaind largely unexplored. In the present study, we analyzed the karyotype and meiotic behaviour during microsporogenesis in accessions of edible chrysanthemum. This information can be useful in cultivar improvement, as well as in elucidation of the evolution of the species. The three edible cultivars studied all had an intermediate type of interphase nucleus, and their mitotic prophase chromosomes were of the interstitial type. The chromosome number of "Baohuatangyijin" (Bn) varies from 55 to 62. "Zifengmudan" (Zn) has the karyotype 2n = 54 = 38m + + 12sm + 4st, while "Jingxingxiying" (Jg) has 2n = 55 = 38m + 15sm + 2st. Male meiosis was largely normal. Mean pairing configuration ofZn at diakinesis and metaphase I was 0.941 + + 25.07II + 0.14III + 0.63IV, while for Jg, the equivalent was 1.32I + 24.64II + 0.16III + 0.85IV + 0.05V + + 0.04VI. Chromatid separation was normal during anaphase I and anaphase II in most meiocytes. All three edible chrysanthemums appear to be allopolyploid, and the edible type is probably more primitive than the ornamental type. However, the edible type is probably more closely related to the ornamental than to the medicinal type.

Comparative karyomorphological studies in three species of Dracocepharum L. (Lamiaceae) in Altai Mountains, Russia and Mongolia

Karyomorophology at the resting nuclei, mitotic prophase and metaphase chromosomes in three species of Dracocepharum were studied. They had commonly the resting nuclei of the complex chromocenter type, the mitotic prophase chromosomes of the proximal type, and the mitotic metaphase chromosomes had 2n=12 for D. peregrinum, 2n=10 for D. nutans and 2n=24 for D. origanoides. These chromosome numbers were verified with the previous reports. The karyotype formula of three species had 2n=12=8m+4sm for D. peregrinum, 2n=10=8m+2sm for D. nutans and 2n=24=14m+10sm for D. origanoides, and chromosome sizes for D. peregrinum is a little smaller one compare with D. nutans and D. origanoides.

Influence of cyclin type and dose on mitotic entry and progression in the early Drosophila embryo

Cyclins are key cell cycle regulators, yet few analyses test their role in timing the events that they regulate. We used RNA interference and real-time visualization in embryos to define the events regulated by each of the three mitotic cyclins of Drosophila melanogaster, CycA, CycB, and CycB3. Each individual and pairwise knockdown results in distinct mitotic phenotypes. For example, mitosis without metaphase occurs upon knockdown of CycA and CycB. To separate the role of cyclin levels from the influences of cyclin type, we knocked down two cyclins and reduced the gene dose of the one remaining cyclin. This reduction did not prolong interphase but instead interrupted mitotic progression. Mitotic prophase chromosomes formed, centrosomes divided, and nuclei exited mitosis without executing later events. This prompt but curtailed mitosis shows that accumulation of cyclin function does not directly time mitotic entry in these early embryonic cycles and that cyclin function can be sufficient for some mitotic events although inadequate for others.

Chromosome characters of two varieties of Ellisiophyllum punnatum (Scrophulariaceae)

Chromosome characters of Ellisiophyllum pinnatum var. typicum (=var. pinnatum) and E. pinnatum var. reptans, were studied. These two varieties had common characters of the resting, mitotic prophase and metaphase chromosomes; complex chromocenter types of the resting chromosomes, interstitial types of the mitotic prophase chromosomes, and the chromosome number of 2n=18 at mitotic metaphase. This species could be diploid if the basic chromosome number x=9 was accepted. The common chromosome number of 2n=18 for the two taxa was reported here for the first time. Their karyotypes were commonly mono-modal decrease in length from the longest to the shortest chromosomes. Ellisiophyllum pinnatum var. reptans had slightly larger chromosomes than E. pinnatum var. typicum had. The chromosome complement in centromeric positions of E. pinnatum var. typicum was m+sm and that of E. pinnatum var. reptans was m+sm+st.

Karyomorphology ofEpimedium(Berberidaceae) and its phylo-genetic implications

Abstract The karyomorphology of 21 species and one variety of Epimedium was investigated in this study, among which 14 species and one variety were reported for the first time. The interphase nucleus and mitotic pro-phase chromosomes were found to be of the complex chromocenter type, and the interstitial type, respectively. The chromosome numbers of all species studied were 2n = 2x = 12. The investigated Epimedium species had a uniform karyotype with 2n = 6m + 6sm, except for three species, E. platyplatum, E. pubescens and E. stellulatum, which had a pair of chromosomes with subterminal centromeres. A secondary constriction was commonly found on the proximal side of the short arm of the chromosome pair I in these species, except for E. pseudowushanense and E. elachyphyllum in which the constriction was on chromosome pair II. The karyotype symmetry of all the investigated species was relatively primitive 2A. Pericentric inversion was observed in E. leptorrhizum, and unequal translocation occured in E. fran...

A karyomorphological study in the monotypic genus Lamiophlomis and five species in Phlomis (Lamiaceae)

The monotypic genus Lamiophlomis (including only L. rotata) and five species of Phlomis in the Lamiaceae were karyornorphologically studied. The interphase nuclei are all categorized to be round prochromosome type, and the mitotic-prophase chromosomes are all categorized to be interstitial type. The karyotype formulae are as follows: L. rotata, 2n=2x=22=18m+4sm; R umbrosa, 2n=2x=22=22m; P ruptilis, 2n=2x=22=22m; P betonicoides, 2n=2x=22=22m; P melanantha, 2n=2x=22=22m(2sat); P strigosa, 2n=6x=66= 60m+ 6sm. The basic chromosome number of Lamiophlomis is confirmed to be x=11, the same as that of Phlomis sect. Phlomoides, which shows that Lamiophlomis rotata should be better treated as a species of Phlomis.

Comparative chromosomal characters of three Japanese species in Chelonopsis, Lamiaceae

Three species of Chelonopsis in Japan were studied regarding their chromosome characters at resting and mitotic prophase and metaphase stages. They had commonly the resting nuclei of the complex chromocenter type, the mitotic prophase chromosomes of the proximal type and the mitotic metaphase chromosomes of 2n=32. Those chromosome numbers were reported here for the first time. The three species indicated quite similar karyotypes with respect to size, centromeric position and monomodal, gradual decrease in length from the largest to the smallest chromosomes.

Chromosome morphology of 12 species and one variety of Lachenalia and five species of closely related, allied genera (Liliaceae)

Somatic chromosomes in 12 species and one variety of Lachenalia and their closely related, two species of Massonia and three species of Polyxena, all in the Liliaceae, were studied. The resting nuclei of all of the taxa studied were commonly classified as the round prochromosome type. The mitotic prophase chromosomes of the taxa studied were commonly classified as the proximal type. However, their chromosome numbers varied from 2n=14, 16, 18, 22, 24, 26 to 28. The chromosome numbers of 2n = 14 in Lachenalia algoensis, L. aloides ‘Lutea’, and L. longibracteata; 2n = 18 in L. latimerae; and 2n = 28 in Massonia pustulata and Polyxena longituba were reported here for the first time. The 13 taxa of Lachenalia studied were classified karyotypically into six groups. The two species of Massonia studied showed commonly the bimodal karyotype with four large chromosomes and the three species of Polyxena studied showed commonly the bimodal karyotype with three large chromosomes. The species of Massonia displayed much larger chromosomes at mitotic metaphase than those of the other two genera.

A Cytological Study on three Species of Colocasia (Araceae) from Yunnan

Chromosome numbers and karyotypes of three Colocasia species from Yunnan were reported. Their karyotypes were as follows: 2n = 2x = 28 = 22m (1 sat) + 6sm for C. gongii; 2n = 2x = 28 = 20m + 8sm for C. gaoligongensis; 2n = 2x = 28 = 20m + 8sm for C. gigantea. Common karyomorphological characteristics of three species examined were: (1) the simple chromocenter type of the resting chromosomes and the proximal type of the mitotic prophase chromosomes; (2) the chromosome number 2n = 28 and (3) the chromosome complement of m- and sm-chromosomes. x = 14 was confirmed as the basic chromosome number of Colocasia. There were differences among species in the number of in- and sm-chromosomes as well as satellite.

A model for chromosome structure during the mitotic and meiotic cell cycles.

The chromosome scaffold model in which loops of chromatin are attached to a central, coiled chromosome core (scaffold) is the current paradigm for chromosome structure. Here we present a modified version of the chromosome scaffold model to describe chromosome structure and behavior through the mitotic and meiotic cell cycles. We suggest that a salient feature of chromosome structure is established during DNA replication when sister loops of DNA extend in opposite directions from replication sites on nuclear matrix strands. This orientation is maintained into prophase when the nuclear matrix strand is converted into two closely associated sister chromatid cores with sister DNA loops extending in opposite directions. We propose that chromatid cores are contractile and show, using a physical model, that contraction of cores during late prophase can result in coiled chromatids. Coiling accounts for the majority of chromosome shortening that is needed to separate sister chromatids within the confines of a cell. In early prophase I of meiosis, the orientation of sister DNA loops in opposite directions from axial elements assures that DNA loops interact preferentially with homologous DNA loops rather than with sister DNA loops. In this context, we propose a bar code model for homologous presynaptic chromosome alignment that involves weak paranemic interactions of homologous DNA loops. Opposite orientation of sister loops also suppresses crossing over between sister chromatids in favor of crossing over between homologous non-sister chromatids. After crossing over is completed in pachytene and the synaptonemal complex breaks down in early diplotene (= diffuse stage), new contractile cores are laid down along each chromatid. These chromatid cores are comparable to the chromatid cores in mitotic prophase chromosomes. As an aside, we propose that leptotene through early diplotene represent the 'missing' G2 period of the premeiotic interphase. The new chromosome cores, along with sister chromatid cohesion, stabilize chiasmata. Contraction of cores in late diplotene causes chromosomes to coil in a configuration that encourages subsequent syntelic orientation of sister kinetochores and amphitelic orientation of homologous kinetochore pairs on the spindle at metaphase I.

Karyomorphology of Podocarpus s.l. in China and its systematic significance

Investigated in the present paper is the karyomorphology of 7 species in 3 sections of Podocalpus s.1. from Yunnan province of China. All species commonly showed the mitotic prophase chromosomes of the same interstitial type, but different resting nuclei type. The resting nuclei were found the gradient type for Sect. Dacrycarpus, the simple chromocenter type for Sect. Nageia and the complex chromocenter type for Sect. Podocarpus respectively. The karyotype formulae were 2n=20=16M+4SM for Podocarpus imbricatus, 2n=26=9M+17SM for P. nagi, 2n=26=17M+9SM for P. wallichiana, 2n=26=13M+13SM for P. fleuryi, 2n=38=19M+3SM+2ST+8T for P. macrophyllus var, angustifolius, 2n=38=18M+10SM+2SM+8T for P. forestii, and 2n=38=20M+10SM+8T for P. neriifolius respectively. The karmorphology of 3 sections in Podocarpus, especially the resting nuclei and basic chromosome number, together with the other data, justified their generic status in the family.

Karyomorphology of Biebersteinia Stephan (Geraniaceae) and its systematic and taxonomic significance

The systematic and taxonomic position of Biebersteinia Stephan has long been in dispute. The present paper describes for the first time the karyomorphology of two species in Biebersreinia Stephan. Both species commonly showed the interphase nuclei of the simple chromocenter type and the mitotic prophase chromosomes of the interstitial type. The karyotype formulae of both B. heterostemon and B. odora were 2n=10=2m(2sec)+8sm(2sec), belonging to the 3A type of Stebbins＇ classification. The karyotype of this genus is recorded for the first time. The basic chromosome numbers of four of the five known species of Biebersteinia have been recorded as x=5. The combination of resting nuclei of the simple chromocenter type, mitotic prophase chromosomes of the interstitial type, two pairs of chromosomes with four obvious secondary constrictions at the mitotic prophase and metaphase stages, and the peculiar 3A karyotype in Biebersteinia can be regarded as the karymorphological marker of this genus. The karyomorphological data presented here do not support the traditional grouping of this genus in Geraniaceae. The unique karyomorphology of Biebersteinia justifies its familiar or ordinal status, which is congruent with embryological, anatomical, chemical and molecular data. The systematic position of Biebersteinia needs further study.

Chromosome no. 1 of Crepis capillaris shows defined 3D-shapes in mitotic prophase.

The shape of mitotic prophase chromosomes has been studied in root tip nuclei by confocal microscopy and 3D-image analysis. Crepis capillaris chromosome no. 1 was used as a test object. Chromosome conformation was studied in early, mid- and in late prophase. In mid- and late prophase, individual chromosomes could be distinguished on the basis of their length. Early prophase chromosomes could not be distinguished as individuals. The central axes of prophase chromosomes were traced with an automated computer procedure and then represented as a string of 3D coordinates. This representation facilitated measurement along the chromosome axis of shape parameters such as curvature (amount of bending), torsion (helical winding) and torsion sign (helical handedness). Stretches of early prophase chromosomes showed full helical turns, which could be left- or right-handed. In the later prophase stages curvature and torsion were statistically analysed. Our data on 40 midprophase chromosomes no. 1 show that they are still highly curved, but full helical turns were no longer found. Instead, an overall meandering pattern was observed. In late prophase, one central loop persisted, flanked by two preferential regions of high curvature.

Nucleolus, nucleolar chromosomes, and nucleolus-associated chromatin from early diplotene to dictyotene in the human oocyte.

The shape, relationships, relative DNA content, and nucleolar activity of the short arm of acrocentric bivalents were studied in human oocytes from early diplotene to dictyotene. At the beginning of diplotene, the short arms of the previously paired chromosomes were again separated and displayed the same morphological features as in mitotic prophase chromosomes. They were connected only with the nucleolus. In situ hybridization and silver staining showed that the nucleolar organizer regions (NORs) were located in the peripheral region of the nucleolus. Tritiated-uridine incorporation was active. At birth, the relationships of the acrocentric short arms showed increasing complexity. The chromosomes ended in nucleolus-associated chromatin blocks of irregular shape, containing large quantities of DNA as demonstrated by intense binding of 3H-actinomycin D. The number of chromosomes converging on these chromatin blocks exceeded the number of acrocentrics, suggesting that heterochromatic regions of other chromosomes were associated with the short arm of acrocentrics. In the electron microscope, the NORs were represented by fibrillar centers located on the periphery of the nucleolus and consistently connected with the blocks of dense chromatin. These relationships remained unchanged in the primordial oocyte in the adult ovary. Persistence of 3H-uridine uptake showed that the oocyte was not at a "resting" stage. The possible cytogenetic consequences of these observations are discussed.