Bivalents In Metaphase Research Articles

Bionomics and Karyotypic analysis of two species of Caccobius (Scarabaeinae: Scarabaeidae: Coleoptera) detected by standard staining, C-banding and AgNOR-banding

Out of 16 species of caccobius available in India, 9 are found in Haryana and 6 in Kurukshetra. The Karyotypic characterisation of two species of Caccobius, C. ultor and C. vulcanus belonging to subfamily Scarabaeinae was undertaken using standard staining, silver staining and C-banding. Both of the species were comprised of 20 chromosomes in karyotype with meioformula, 9AA+Xyp. Modal chromosome number and meta-, submeta- centric nature revealed the conservative nature of the subfamily Scarabaeinae. The analysis of constitutive heterochromatin (CH) revealed small centromeric bands in spermatogonial metaphase and small blocks located in the terminal regions of dumb bell shaped bivalents in metaphase I. At the pachytene stage of prophase I, silver staining revealed dense spots associated with nucleolar organizer regions. In addition to this, the Chiasma frequency and terminalisation coefficient were also calculated, illustrating the close relationship of Caccobius ultor and C. vulcanus with other Scrabaeinae species. In beetles as well as in other insects, the chromosome structure, pattern of constitutive heterochromatin distribution, and position of the nucleolar organizer region are all key factors in speciation.

Derived alleles of two axis proteins affect meiotic traits in autotetraploid Arabidopsis arenosa

Polyploidy, which results from whole genome duplication (WGD), has shaped the long-term evolution of eukaryotic genomes in all kingdoms. Polyploidy is also implicated in adaptation, domestication, and speciation. Yet when WGD newly occurs, the resulting neopolyploids face numerous challenges. A particularly pernicious problem is the segregation of multiple chromosome copies in meiosis. Evolution can overcome this challenge, likely through modification of chromosome pairing and recombination to prevent deleterious multivalent chromosome associations, but the molecular basis of this remains mysterious. We study mechanisms underlying evolutionary stabilization of polyploid meiosis using Arabidopsis arenosa, a relative of A. thaliana with natural diploid and meiotically stable autotetraploid populations. Here we investigate the effects of ancestral (diploid) versus derived (tetraploid) alleles of two genes, ASY1 and ASY3, that were among several meiosis genes under selection in the tetraploid lineage. These genes encode interacting proteins critical for formation of meiotic chromosome axes, long linear multiprotein structures that form along sister chromatids in meiosis and are essential for recombination, chromosome segregation, and fertility. We show that derived alleles of both genes are associated with changes in meiosis, including reduced formation of multichromosome associations, reduced axis length, and a tendency to more rod-shaped bivalents in metaphase I. Thus, we conclude that ASY1 and ASY3 are components of a larger multigenic solution to polyploid meiosis in which individual genes have subtle effects. Our results are relevant for understanding polyploid evolution and more generally for understanding how meiotic traits can evolve when faced with challenges.

Altered bivalent positioning in metaphase I human spermatocytes from Robertsonian translocation carriers.

The study aims to determine whether there is an altered bivalent positioning in metaphase I human spermatocytes from Robertsonian translocation carriers. Metaphase I human spermatocytes from three 45,XY,der(13;14)(q10;q10) individuals and a 45,XY,der(14;15)(q10;q10) individual were analyzed. Proximity relationships of bivalents were established by analyzing meiotic preparations combining Leishman staining and multiplex-FISH procedures. Poisson regression model was used to determine proximity frequencies between bivalents and to assess associations with chromosome size, gene density, acrocentric morphology, and chromosomes with heterochromatic blocks. The hierarchical cluster Ward method was used to characterize the groups of bivalents with preferred proximities in a cluster analysis. Bivalent groups obtained were individually compared with those obtained in normal karyotype individuals evaluated in a previous study. A total of 1288 bivalents were examined, giving a total of 2289 proximity data. Only four positive significant proximities were detected for each type of Robertsonian translocation. Significant bivalent associations were only observed by small-size chromosomes for MI,22,XY,III(13q14q). These results were clearly divergent from 46,XY individuals. Moreover, cluster analysis revealed that about 30% of the bivalents showed changes in their proximity relationships in metaphase I. The territorial organization of bivalents in metaphase I human spermatocytes changes in the presence of a Robertsonian translocation.

Microsporogenesis in Brachiaria brizantha (Poaceae) as a selection tool for breeding

The genus Brachiaria comprises more than 100 species and is the single most important genus of forage grass in the tropics. Brachiaria brizantha, widely used in Brazilian pastures for beef and dairy production, is native to tropical Africa. As a subsidy to the breeding program underway in Brazil, cytological studies were employed to determine the chromosome number and to evaluate microsporogenesis in 46 accessions of this species available at Embrapa Beef Cattle (Brazil). Thirty-four accessions presented 2n = 36; seven had 2n = 45, and five had 2n = 54 chromosomes. Based on the higher level of chromosome association observed in diakinesis, in tetra-, penta-, and hexavalents, respectively, it was concluded that they are derived from x = 9; consequently, these accessions are tetra- (2n = 4x = 36), penta- (2n = 5x = 45), and hexaploids (2n = 6x = 54). The most common meiotic abnormalities were irregular chromosome segregation due to polyploidy. Chromosome stickiness, abnormal cytokinesis, non-congressed bivalents in metaphase I and chromosomes in metaphase II, and chromosome elimination were recorded at varying frequencies in several accessions. The mean percentage of meiotic abnormalities ranged from 0.36 to 95.76%. All the abnormalities had the potential to affect pollen viability by generating unbalanced gametes. Among the accessions, only the tetraploid ones with less than 40% of abnormalities are suitable as pollen donors in intra- and interspecific crosses. Currently, accessions with a high level of ploidy (5 and 6n) cannot be used as male genitors in crosses because of the lack of sexual female genitors with the same levels of ploidy.

Contribution to the cytotaxonomy of Oryzopsis (Poaceae)

Meiotic studies were performed in twelve populations of four Oryzopsis species (O. pubiflora, O. lateralis, O. holciformis var. longiglomis and O. barbellata) to obtain data on the ploidy level and cytological evolution of the genus. The chromosome number 2n=2x=24 was revealed in all the species and populations studied. The present and other studies show the occurrence of two basic chromosome numbers in the genus, i.e. x=11 and x=12. Although Oryzopsis species and populations studied are diploid and are expected to form only bivalents in metaphase of meiosis-I, quadrivalents were observed in O. pubiflora and O. lateralis, possibly due to the occurrence of heterozygote translocations. B-chromosomes of 0–2 were observed in all species and populations studied. This is the first report of the occurrence of B-chromosomes in the genus Oryzopsis. Several meiocytes showed the presence of double chromosome number in O. lateralis, and multipolar cells were observed in populations of O. barbellata, O. lateralis and O. holciformis var. longiglomis. The occurrence of large pollen grains (possibly unreduced) was observed along with smaller (normal) pollen grains in these species. Significant differences observed in chiasma frequency and distribution among studied species may be of use in species delimitation. The Kakan population differed significantly from the other populations of O. lateralis in meiotic characteristics. If such cytological differences are accompanied by morphological variation (under investigation), we may consider this population as a new variety or subspecies.

Contribution to Cytotaxonomy of Iranian Cirsium (Asteraceae)

A meiotic study was performed on 21 populations of 17 Cirsium species growing in Iran. The species of C. spectabile, C. congestum, C. strigosum, C. ciliatum, C. osseticum, C. aduncum, C. haussknechtii, C. turkestanicum, C. echinus, C. obvallatum, C. libanoticum, C. alatum, C. echinus, C. obvallatum, C. libanoticum, C. hygrophilum and C. arvense had 2n=2x=34 chromosome number, while the species of C. lappaceum, C. vulgare and C. elodes showed 2n=4x=68. The chromosome numbers of C. spectabile, C. strigosum, C. haussknechtii, C. lappaceum, C. turkestanicum and C. libanoticum are new to science and a new polyploidy level (4x) has been reported for C. elodes. The ANOVA test revealed significant differences for chiasma frequency and chromosome pairing among the species studied and the Pearson coefficient of correlation determined showed significant positive correlation between intercalary chiasmata and the mean number of quadrivalents. Although diploid species and populations are expected to form only bivalents in metaphase I, quadrivalents were formed in C. arvense, C. ciliatum, C. congestum, C. echinus, C. strigosum and C. libanoticum possibly due to the occurrence of heterozygote translocations. Interestingly enough, tetraploid species of C. lappaceum did not form any quadrivalents showing diplontic behavior. The occurrence of large pollen grains (possibly 2n pollen grains) was observed along with smaller (normal) pollen grains in species and populations showing tripolar cells. Cytological characteristics may be used in species delimitation in Cirsium but may not be used in sectional delimitation of the genus.

Meiosis in Solanum phureja

Meiosis and pollen mitosis were studied in a clone of Solanum phureja in order to elucidate the generally high frequency (about 90 %) of tetraploid progeny in tetraploid X diploid crosses involving S. phureja. The first meiotic division was normal with 12 bivalents in metaphase and apparently normal chromosome disjunction. The second meiotic division showed normal metaphases with 12 chromosomes in each of the two spindles, along with cells showing a bi- or tripolar spindle (cell wall formation was simultaneous). At the end of the second division those disturbances resulted in unreduced cells either with two diploid nuclei or with one diploid and two haploid nuclei along with the normal tetrads with four haploid nuclei. The frequency of unreduced gametes was about 50 %. First and second pollen mitoses were also represented by normal haploid as well as unreduced diploid cells. Hence, the high frequency of tetraploid offspring in Solanum tuberosum X S. phureja crosses could be caused by selective fertilization with unreduced diploid pollen grains.

Late prophase and first metaphase in female meiosis of Drosophila melanogaster

Details of the critical stages that precede the appearance of the metaphase bivalents in the female Drosophila melanogaster were studied in a comparison between whole-mount preparations and squash preparations. At the end of stage S13 the nuclear membrane breaks down, and the bivalents leave the chromocenter and become orientated on the first meiotic spindle. In stage S14 a metaphase I plate with separate bivalents is formed. A renewed survey of female meiosis in Drosophila melanogaster in relation to egg follicle stages is presented.

Cytomixis and Unreduced Pollen Grain Formation in Alopecurus L. and Catbrosa Beauv. (Poaceae)

Meiotic studies were performed on the populations of four Alepecurus L. species and varieties as well as five populations of two Catabrosa species. Alopecurus textilis showed 2n=8x=56 chromosome number, the varieties of A. myosuroides var. myosuroides and A. myosuroides var. breviaristatus showed 2n=2x=14 and A. arundinaceus possessed 2n=6x=42. Catabrosa aquatica and C. capusii showed 2n=4x=20 chromosome number. The chromosome numbers of A. textilis, A. myosuroides var. myosuroides and A. myosuroides var. breviaristatus and C. capusii are new to science, while hexaploid level is new for A. arundinaceus. Tetraploid and octaploid species of Alopecurus and Catabrosa studied formed bivalents in metaphase of meiosis-I, which is considered a diplontic behavior for polyploid species. Grouping of the species by clustering methods based on relative cytogenetical characteristics showed good separation between Alopecurus and Catabrosa species indicating the cytogenetic distinctness of these two grass genera. Cytomixis and chromosome migration occurred in most of the species and populations studied forming aneuploid and polyploid meiocytes. Unreduced pollen grains were formed possibly as a result of cytomixis in the species studied.

Species Relationships in Hordeum: Cytology and RAPD Analyses

Cytological and molecular studies were performed on 10 Hordeum species of Iran. The species studied showed the occurrence of 2n=2x=14, 2n=4x=28 and 2n=6x=42. They formed mainly bivalents in metaphase with normal chromosomes segregation during anaphase and telophase stages, except in few cases of laggard chromosomes formation and chromosome stickiness observed in H. bulbosum. H. bulbosum and H. leporinum showed 0–2 B-chromosomes which were smaller than A-chromosomes and did not pair with them out of 20 RAPD primers used 11 primers produced 18 reproducible polymorphic bands. Specific bands were observed in some of the species or populations while, some bands occurred in all the species except one showing the species genetic differences. Clustering of the species based on cytological and RAPD data partly produced similar results, separating H. vulgare and H. spontaneum from each other. The species of H. marinum, H. glaucum and H. leporinum from the sect. Hordeastrum were grouped together, while H. violaceum H. bogdanii and H. brevisubulatum, from the sect. Stenostachys were placed in different clusters separated from each other. H. bulbosum and H. vulgare showed a close relationship, while H. spontaneum, H. distichon and H. vulgare were placed close to each other supporting their taxonomic position in Flora Iranica.

Cytogenetical studies of some species of the genus Secale L. (Poaceae) in Iran

Abstract Karyotypic study of 15 populations and meiotic analysis of 7 populations belonging to 4 Secale subspecies and varieties grown wild in Iran were performed for the first time. The subspecies and varieties studied possessed 2n = 2x = 14 chromosome number, varied in their karyotypic formulae and symmetry and in their total chromatin length as well as size of the chromosomes, indicating the occurrence of both structural and quantitative changes in their genomes during the species diversification. The species studied formed mainly bivalents in metaphase of meiosis-I with a low amount of univalents and quadrivalents.

Chromosome Pairing and Chiasma Formation in Some Olive (Olea europaea L.) Cultivars of Iran

Cytogenetic characteristics of 11 olive cultivars were studied considering their chromosome pairing and segregation. The cultivars studied possessed 2n=4x=46 chromosome number and formed only bivalents in metaphase of meiosis-I. The cultivars differed significantly in their chiasma frequency and distribution as well as chromosome pairing indicating partly their genetic distinctness. Meiotic abnormalities including laggard chromosomes and chromosome stickiness occurred in the cultivars studied. B-chromosomes, cytomixis and unreduced pollen grains were observed in some of the cultivars. Clustering and ordination of the olive cultivars based on cytogenetic characteristics showed distinctness of these cultivars. B-chromosomes and unreduced pollen grain formation are new in olive cytogenetics.

Cytogenetic study of Amaranthus L. species in Iran

Cytogenetic analysis of 12 populations of 10 Amaranthus L. species and varieties revealed the presence of 2n=32 and 34 chromosome number in them. The species studied showed a normal meiosis forming manly bivalents in metaphase of meiosis I. A post pachytene diffuse stage occurred in all the species possibly as a means of adaptation to adverse environmental conditions. ANOVA test revealed significant differences in relative cytogenetic characteristics including chiasma frequency and distribution as well as chromosome pairing among the studied species, indicating their genomic differences. Grouping of the species based on cytogenetic data almost agrees with the clustering of Amaranthus species based on morphological and protein data.

Reproductive Behavior of Diploid and Allotetraploid Rhododendron L. ‘Fragrant Affinity’

Wide hybridization can lead to recombination of diverse traits and creation of unique phenotypes, but the resultant hybrids are often sterile as is the case with the intersubgeneric hybrid Rhododendron L. ‘Fragrant Affinity’. Sterility in wide hybrids can either be genic or chromosomal; the latter may be overcome by induction of polyploidy, which can restore chromosome homology and fertility. Cytologic studies of ‘Fragrant Affinity’ appear to support the presence of bridges between bivalents in metaphase I and laggard chromosomes in anaphase I. In the current study, an allotetraploid form of R. ‘Fragrant Affinity’ was developed using oryzalin (4-(dipropylamino)-3, 5-dinitro-benzenesulfonamide) as a mitotic inhibitor and chromosomal doubling agent. Genome sizes (2C) were determined using flow cytometry and found to be ≈1.6 and 3.2 pg for the diploid and allotetraploid, respectively. Pollen viability, determined by staining and germination tests, was 4% and 0%, respectively, for the diploid and 68% and 45%, respectively, for the allotetraploid. No seeds were produced when the diploid R. ‘Fragrant Affinity’ was used as a pistillate parent when pollinated with pollen from viable diploid and tetraploid parents. The allotetraploid produced viable seeds and seedlings when pollinated with pollen from either diploid or tetraploid parents, including self-pollination, demonstrating restored male and female fertility.

Rod-Shaped Bivalents indicate new assemblage among Anatolian Water Frog Populations

AbstractThe general features of the mitotic and meiotic chromosomes analysed in 91 frogs belonging to nine water frog populations distributed in Southwest Anatolia. The differences found in mitotic and meiotic chromosomes revealed the existence of two groups among the populations: the first "Aegean Group" includes those from Izmir, Bulca, Pazarağaç, and the second – "Lake District Group" from Eber, Akşehir, Gelendost, Eğirdir, Gölcük, and Beyşehir populations. The major distinction appeared in the number of the rod-shaped bivalents in metaphase I, with only one in the "Aegean Group" compared to one or two in the "Lake District Group". This result indicates a new assemblage among Anatolian water frogs and strengthens the suggestion that the "Lake District Group" that have one or two rod shaped bivalents in metaphase I due to the inclusion of hybrid lineages containing both parental genomes. It is clear that at least two separate species are present in Anatolia; one of them is possibly Rana ridibunda from the north and the second is closer to the Balkan species Rana epeirotica and Rana shqiperica.

Cytogenetic Studies in the Rare South American Lathyrus hasslerianus Burk. (Leguminosae)

A detailed analysis of the karyotype and the meiotic behavior of the South American endemic Lathyrus hasslerianus is provided in this study. The karyotype obtained is the most asymmetrical of section Notolathyrus, which together with the particular morphological characters and ecological requirements supports a derived state of this species. Meiotic analysis showed the occurrence of univalents and out of plate bivalents in metaphase I, which ultimately leads to the formation of micromicrospores or micronuclei at the sporad stage. Mechanisms of aberrant sporad formation are discussed. Even though, pollen viability was reduced, it does not compromise the species fertility as shown by the analysis of the seed set.

Meiotic chromosome behaviour in an allotriploid derived from an amphidiploid × diploid mating in Cucumis

AbstractA synthetic amphidiploid species Cucumis hyriviis Chen & Kirkbride (2n = 4x = 38; genome designated as HHCC) has recently been created from an interspecific mating between C. sativus L. (2n = 2x = 14: genome designated as CC) and C. hystrx. Chakr. (2n = 2x = 24; genome designated as HH). This amphidiploid is resistant to root knot nematode, tolerant to low irradiance, and has higher nutritional value than standard processing cucumber cultivars. An allotriploid (2n = 3x = 26; HCC) was derived from a cross between C. sativus L. and C. hytivus Chen & Kirkbride. Diploid meiotic behaviour in C. sativus and C. hystrix involves the development of seven and 12 metaphase bivalents respectively. In the derived allotriploid. univalents. bivalents, and trivalents (at relatively low frequency) were observed at metaphase I indicating that some homeologues from the C and H genomes can synapse. Based on a comparative karyotype analysis of cucumber (i.e. chromosome size and pairing behaviour) and aliotriploid plants, the seven bivalents observed at metaphase I were ascertained to be cucumber homologues, while the 12 univalents were of C. hystrix origin thus confirming the allotriploid karyotypic constitution to be HCC. On average, the frequency of trivalents was 0.24 at diakinesis and 0.22 in 100 meiocytes at metaphase I. indicating the possibility of genetic exchange due to the homoeology between the C and H genomes. After simultaneous cytokinesis, only polyads were observed in pollen mother cells (PMCs) at telophase II, which led to the production of sterile pollen grains. Multi‐polarization of chromosomes was dominant at anaphase II. However. in about 20% PMCs. chromosomes separated to form a 7C + 1‐2H complement, suggesting a possible method for the production of alien addition cucumber‐C hystrix lines through further backcrossing of the allotriploid to diploid cucumber.

Identification of meiotic anomalies with multiplex fluorescence in situ hybridization: Preliminary results

To characterize meiotic anomalies in infertile men by multiplex fluorescence in situ hybridization (M-FISH) and to determine whether synaptic problems affect specific bivalents or whether anomalies are random. Analysis of meiotic preparations with standard techniques and M-FISH. Assisted reproduction centers and Universitat Autònoma de Barcelona. Three fertile men undergoing vasectomy, four sterile patients with oligoasthenoteratozoospermia, and one patient with a Robertsonian translocation t(13;14). Unilateral testicular biopsy in controls and patients with oligoasthenoteratozoospermia and collection of a semen sample from the translocation carrier. Identification of bivalents in metaphase I and chromosomes in metaphase II and characterization of chromosome abnormalities. All bivalents in metaphase I and all chromosomes in metaphase II could be identified. In controls and in one patient with oligoasthenoteratozoospermia, meiosis was normal. Other patients with oligoasthenoteratozoospermia showed different types of anomaly: desynapsis, breaks, precocious XY separation, or cryptic reorganizations. The Robertsonian translocation t(13;14) was easily identified. Results confirm the high incidence of synaptic errors in oligoasthenoteratozoospermia patients. Bivalents in metaphase I and chromosomes in metaphase II were individually identifiable. Nondisjunctional errors or small reorganizations overlooked in classic meiotic preparations were identified. Synaptic anomalies seem to affect meiotic bivalents at random.

Experimentally Induced Autotetraploidy and Allotetraploidy in Two Japanese Pond Frogs

We examined cytogenetic features and reproductive capacity in newly arisen tetraploid amphibians. Autotetraploids were produced by suppressing second polar body formation in haploid eggs of diploid females of Rana nigromaculata inseminated with diploid sperm of autotetraploid R. nigromaculata. Allotetraploids were also produced by suppressing second polar body formation in haploid eggs of diploid females of Rana porosa brevipoda inseminated with diploid sperm of autotetraploid R. nigromaculata. In male R. nigromaculata autotetraploid offspring, mostly quadri- and bivalents were found in Metaphase I, and 26 dyads were seen in Metaphase II. Autotetraploid males were then mated with autotetraploid females, and most of the resultant offspring were tetraploids possessing four chromosome sets of diploid R. nigromaculata. Male allotetraploid offspring showed 26 bivalents in Metaphase I and 26 dyads in Metaphase II. A large number of the offspring resulting from crosses between allotetraploid males and females were tetraploids having chromosome sets of diploid R. nigromaculata and diploid R. p. brevipoda. These results seem to indicate that, if such tetraploids develop a distinguishing premating mechanism, they should continue as a sexual fertile species in one generation and coexist with their diploid parental species.

New occurrence of microchromosomes B in Moenkhausia sanctaefilomenae (Pisces, Characidae) from the Paraná River of Brazil: analysis of the synaptonemal complex.

The Moenkhausia sanctaefilomenae specimens showed a karyotype consisting of 2n = 50 chromosomes with 12 metacentrics, 36 submetacentrics and two subtelocentrics. In addition to the basic karyotype, all the males specimens have cells ranging from zero to two B microchromosomes in mitotic metaphases. These chromosomes were not observed in the female specimens. C-band analysis showed a distribution pattern of characteristic heterochromatin with interstitial and centromeric blocks. However, the B chromosomes were faintly stained with C-banding and were not fluorescent with CMA3 staining. The meiotic studies showed the formation of bivalents in metaphase I and in pachytene under an optical microscope. Through synaptonemal complex analysis with an electron microscope, the pachytene showed 25 bivalents completely paired and a small bivalent corresponding to the B chromosomes. In the same preparation, one of the B chromosomes was observed in a univalent form. On the basis of pairing behavior and morphology it is assumed that B chromosomes of M. sanctaefilomenae show homology between them and their evolutionary aspects are discussed.