Ring Bivalents Research Articles

First report of chromosome and karyological analysis of Gekko nutaphandi (Gekkonidae, Squamata) from Thailand: Neo-diploid chromosome number in genus Gekko

The karyotypes of red-eyed Gecko are not reported yet. Herein, we describe the karyotypes of red-eyed Gecko (Gekko nutaphandi Bauer, Sumontha & Pauwels, 2008) from Thailand. Gecko chromosome preparations were directly conducted from bone marrow and testis. Chromosomal characteristics were analyzed by Giemsa staining, Ag-NOR banding as well as fluorescence in situ hybridization (FISH) using microsatellites d(GC)15 probe. The results showed that the number of diploid chromosomes is 2n=34, while the fundamental number (NF) is 46 in both males and females. The types of chromosomes were 4 large metacentric, 6 large submetacentric, 2 medium telocentric, 2 small metacentric and 20 small telocentric chromosomes. The results of conventional Giemsa staining presented the diploid chromosome number differentiation even in the same genus. NORs are located at the secondary constriction to the telomere on the long arm of chromosome pair 5. There are no sex differences in karyotypes between males and females. FISH with d(GC)15 sequences were also displayed at the telomeres of most other chromosomes. We found that during metaphase I the homologous chromosomes showed synapsis, which can be defined as 19 ring bivalents and 17 haploid chromosomes (n=17) at metaphase II as a diploid species. The karyotype formula is as follows: 2n (34) = L4m+L6sm+M2t+S2m+S20t.

Molecular cytogenetic study on the plants of Elymus nutans with varying fertility on the Qinghai-Tibet Plateau

A molecular cytogenetic investigation was conducted on plants of the allohexaploid species Elymus nutans with varying fertility on the Qinghai-Tibet Plateau. Molecular karyotyping revealed that chromosome variants were distributed unevenly among genomes and among different homologue chromosomes in each genome. The plants with varying fertility exhibited significantly higher numbers of chromosome variants than did the normal fertility samples, although both kinds of plants showed the same pattern of high-to-low polymorphism from the Y to St and H genomes. Heterozygosis and karyotype heterozygosity in the plants with varying fertility were 3- and 13-fold higher than those in normal samples, respectively. Significant negative correlations were found not only between seed setting rates and total genome heterozygosity but also between seed setting rates and heterozygosity of each genome in the plants of varying fertility. Chromosome pairing analysis was performed using genomic in situ hybridization in selected plants of different fertility levels. The pairing of chromosomes at meiotic metaphase I was mostly bivalent, although univalent, trivalent, quadrivalent, and other polyvalents also occurred; in addition, chromosome configuration forms and frequencies varied among the studied samples. ANOVA results showed that the average number of ring bivalents in the Y genome was significantly higher than those in the St and H genomes. Significant positive correlations between pollen grain fertility and ring bivalent number were found in the St and H genomes but not in the Y genome. Furthermore, chromosome configuration parameters (total bivalents, numbers of ring and rod bivalents) were found to be significantly correlated with heterozygosity and seed setting rates in the St and H genomes, respectively, but not in the Y genome. It was inferred that the seed setting rate and pollen grain fertility in E. nutans are strongly influenced by the heterozygosity of each genome, but the Y genome differs from the St and H genomes due to chromosome pair alterations. The St and H genomes may contain more chromosome structural variations than the Y genome in E. nutans.

Molecular Cytogenetic Analysis and Meiotic Pairing Behavior of Progenies Originating from a Hexaploid Triticale (×Triticosecale, Wittmack) and Bread Wheat (Triticum aestivum, L.) Cross

The chromosomal constitution of 9 dwarf (D) and 8 semidwarf (SD) lines derived by crossing hexaploid Triticale line NA-75 (AABBRR, 2n = 6x = 42) with Triticumaestivum (AABBDD, 2n = 6x = 42) cv. Chinese Spring was investigated using molecular cytogenetic techniques: fluorescence in situ hybridization and genomic in situ hybridization. A wheat-rye translocation (T4DS.7RL), 8 substitution lines, and a ditelosomic addition line (7RSdt) were identified. In the substitution lines, 1, 2, or 4 pairs of wheat chromosomes, belonging to the A, B, or D genome, were replaced by rye chromosomes. Substitutions between chromosomes belonging to different wheat genomes [5B(5A), 1D(1B)] also occurred. The lines were genetically stable, each carrying 42 chromosomes, except the wheat-rye ditelosomic addition line, which carried 21 pairs of wheat chromosomes and 1 pair of rye telocentric chromosomes (7RS). The chromosome pairing behavior of the lines was studied during metaphase I of meiosis. The chromosome pairing level and the number of ring bivalents were different for each line. Besides rod bivalents, univalent and multivalent associations (tri- and quadrivalents) were also detected. The main goal of the experiment was to develop genetically stable wheat/Triticale recombinant lines carrying chromosomes/chromatin fragments originating from the R genome of Triticale line NA-75. Introgression of rye genes into hexaploid wheat can broaden its genetic diversity, and the newly developed lines can be used in wheat breeding programs.

CRISPR/Cas inactivation of RECQ4 increases homeologous crossovers in an interspecific tomato hybrid.

SummaryCrossover formation during meiosis in plants is required for proper chromosome segregation and is essential for crop breeding as it allows an (optimal) combination of traits by mixing parental alleles on each chromosome. Crossover formation commences with the production of a large number of DNA double‐strand breaks, of which only a few result in crossovers. A small number of genes, which drive the resolution of DNA crossover intermediate structures towards non‐crossovers, have been identified in Arabidopisis thaliana. In order to explore the potential of modification of these genes in interspecific hybrids between crops and their wild relatives towards increased production of crossovers, we have used CRISPR/Cas9‐mutagenesis in an interspecific tomato hybrid to knockout RecQ4. A biallelic recq4 mutant was obtained in the F1 hybrid of Solanum lycopersicum and S. pimpinellifolium. Compared with the wild‐type F1 hybrid, the F1 recq4 mutant was shown to have a significant increase in crossovers: a 1.53‐fold increase when directly observing ring bivalents in male meiocytes microscopically and a 1.8‐fold extension of the genetic map when measured by analysing SNP markers in the progeny (F2) plants. This is one of the first demonstrations of increasing crossover frequency in interspecific hybrids by manipulating genes in crossover intermediate resolution pathways and the first to do so by directed mutagenesis.Significance statementIncreasing crossover frequency during meiosis can speed up or simplify crop breeding that relies on meiotic crossovers to introduce favourable alleles controlling important traits from wild relatives into crops. Here we show for the first time that knocking out an inhibitor of crossovers in an interspecific hybrid between tomato and its relative wild species using CRISPR/Cas9‐mutagenesis results in increased recombination between the two genomes.

Cytogenetic Behavior of Trigeneric Hybrid Progeny Involving Wheat, Rye and Psathyrostachys huashanica

Trigeneric hybrids are commonly used as bridges to transfer genes from some wild species to cultivated wheat and to measure the genomic interaction between donor species. We previously reported that trigeneric germplasms were produced by crossing wheat-Psathyrostachys huashanica amphiploids (PHW-SA, 2n = 8x = 56, AABBDDNsNs) with hexaploid triticale (Zhongsi 828, 2n = 6x = 42, AABBRR). In the present study, chromosome pairing behavior and the genome constitution of the F₄ progenies of wheat-rye-P. huashanica trigeneric hybrids were studied. Cytological analysis showed that the chromosome number of F₄ progenies ranged from 39 to 46, and 57.5% of them had 42 chromosomes. The mean meiotic configuration of F₄ lines was 1.71 univalents, 20.26 bivalents, 0.04 trivalents, and 0.001 quadrivalents per pollen mother cell. Among the lines with 2n = 42, the average pairing configuration was 1.21 univalents, 16.22 ring bivalents, 4.16 rod bivalents, and 0.01 trivalents. This result indicated that these lines were cytologically stable. Other lines with 2n = 39, 40, 41, 43, 44, 45, and 46, bearing a high number of univalents or multivalents, showed abnormal meiotic behavior. Genomic in situ hybridization (GISH) revealed that all F₄ lines had 11-14 rye chromosomes, but no P. huashanica chromosomes. The complete set of 14 rye chromosomes was found in 19 lines. At meiosis, GISH detected 1-6 univalents with hybridization signals of rye in 13 lines. Bivalents with fluorescence signals were identified in each line, ranging from 3 to 7. A quadrivalent with hybridization signals was observed in only 1 line, K13-714-8. Lagging chromosomes, chromosome bridges, micronuclei, and chromosome fragments hybridizing with the probe were not discovered in any of the lines. These results inferred that the behavior of rye chromosomes was normal during meiosis. In addition, 21 lines of 2n = 42 (91.3%) with 12 or 14 rye chromosomes, always contained 6 or 7 bivalents bearing fluorescence signals. This suggested that the rye chromosomes exhibiting complete pairing in these lines were cytologically stable during meiosis and may therefore be considered as new hexaploid triticales. Thus, these lines might be potential materials for further hexaploid triticale improvement.

First report on a multiple sex chromosome system (X<sub>1</sub>X<sub>2</sub>X<sub>3</sub>0) and population variations in the frequency of ring bivalents in Pyrrhocoridae (Hemiptera: Heteroptera)

The family Pyrrhocoridae (Hemiptera: Heteroptera) is characterized by a modal diploid chromosome number of 16 (♂) rang- ing from 12 to 33 and simple (X0), multiple (X 1 X 2 0) and neo-sex chromosome systems (neoX-neoY). Out of about 340 known species, only 22 species belonging to 7 genera have to date been cytogenetically analysed. In the present study, the chromosome complement and meiotic details of one species, Odontopus nigricornis Stal has been revised, whilst that of another species, Antilochus russus Stal has been cytogenetically analyzed for the first time. The diploid chromosome complement of O. nigricornis is 2n (♂) = 25 = 22A + X 1 X 2 X 3 0; the first time this particular multiple sex chromosome system has been reported in the Pyrrhocoridae. Three sex chromosomes mostly remain intimately associated during male meiosis and their number was confirmed at diplotene and anaphase II, where they dissociate slightly to become distinct. Meiosis is post-reductional for sex chromosomes. However, unlike other pyrrhocorids with mul- tiple X chromosomes, the X 1 , X 2 and X 3 lie outside the autosomal ring on the metaphase plate during both divisions. The male diploid chromosome complement of A. russus was found to be 2n = 27 = 26A + X0. Apart from the typical meiotic features of heteropterans, the latter species shows inter- and intra-population variations in frequency of ring bivalents.

Study of the mitotic and meiotic chromosomes of sotol (Dasylirion cedrosanum Trel.)

The genus Dasylirion is a group of plants typically present in the Chihuahuan Desert, perennial, with a dioecious sexual behavior and commonly called sotoles. This genus has been little studied from the biological point of view, and the bases of its reproductive response remain unknown. In this work we studied the chromosome number and meiotic response of Dasylirion cedrosanumin the county of Saltillo, Coahuila, located at the North East of Mexico. For the preparation of mitotic chromosomes, we used a technique based on enzymatic treatment with pectolyase and cellulase, as well as staining with acetocarmin dye. For the study of meiosis, male flower buds were collected, fixed and stained for analysis with the same dye. As a result, the gametic (n = x = 19) and somatic chromosome (2n = 38) numbers of D. cedrosanum are reported for the first time, being consistent with previous findings in other Dasylirion species, which points to a constant ploidy level across the genus. Variation was observed in the morphology and size of the somatic chromosomes, with types ranging from submetacentric to subtelocentric, and sizes oscillating in a range of 4.43 µm, with an average total length of 112.38 µm for the diploid chromosome complement. This shows that the chromosome complementof D. cedrosanom would belong to a 3B classification of Stebins, with a medium variation between chromosome lengths and low chromosome asymmetry. This variation indicates the feasibility of constructing a chromosome ideotype for this species. The meiotic chromosome pairing showed a chromosome behavior consistent with a disomic inheritance characteristic of a diploid species, with prevalence of ring and chain bivalents, typically without pairing abnormalities. Bivalent configurations in all cases were symmetrical. The normal and symmetrical meiotic pairing indicates a balanced production of gametes, and suggests the absence of heteromorphicsex determination.

Karyotype evolution in progress: A new diploid number in Belostoma candidulum (Heteroptera: Belostomatidae) from Argentina leading to new insights into its ecology and evolution

A novel chromosome complement (2n = 14 = 12 + XY/XX; male/female sex chromosomes), male meiosis behaviour, het­ erochromatin characterization, and frequency and distribution of chiasmata are described for the first time in specimens from a natural population of the giant water bug, Belostoma candidulum Montandon, 1903 (Heteroptera: Belostomatidae) from Argentina. To date, specimens of B. candidulum have been reported by other authors in a sample from a natural population from Brazil. Our results dem­ onstrate that Argentinean and Brazilian populations have different diploid numbers and chromosomal features. During male meiosis, autosomal bivalents generally show a single chiasma, behave as telokinetic chromosomes (i.e. kinetic activity is restricted to terminal regions), and divide reductionally at anaphase I; in contrast, the sex chromosomes are achiasmatic, behave as univalents and segregate equationally at anaphase I. Among autosomal bivalents of B. candidulum, one is remarkably larger and may present one or two termi­ nal chiasmata, showing rod, V-shaped and ring configurations. Here we propose a new mode of segregation for ring bivalents, since it is not essential that one of the chiasmata is released during anaphase I because alternative sites for microtubule attachment become functional for the normal chromosome segregation to the poles. Heterochromatin content is very scarce in specimens from Argentinean B. candidulum populations, revealing C ­ positive interstitial and terminal dots in three pairs of autosomes and C ­ blocks at both ends of X chromosome, whereas the Y chromosome is mainly C ­ positive. One of the C ­ positive bands from X and Y chromosomes is DAPI ­ dull/CMA-bright, which could represent the nucleolus organizing region (NOR) detected by fluorescent in situ hybridization (FISH). The location of the NORs in both sex chromosomes allowed us to use them as a cytological marker to describe their behaviour during meiosis. Despite the fact that specimens from the Argentinean and Brazilian populations have been classified as a single species due to their morphological similarity, our results suggest that both populations are chromosomal races or even morphologically ­ identical cryptic species. The results obtained support the hypothesis that karyotype of B. candidulum originated through autosomal fusions and the fusion of the X and Y chromosomes with the ancestral NOR ­ autosomal pair. Lastly, the genus Belostoma represents an excellent model for assessing the main mechanisms involved in the karyotype evolution in organisms with holokinetic chromosomes, from which inferences may be made concerning its broader ecology and evolution.

A study on meiotic behaviour in Paeonia anomala subsp. veitchii, Paeoniaceae

Chromosomal meiotic behaviour in pollen mother cells (PMCs) of Paeonia anomala subsp. veitchii, endemic to China, was investigated in three natural populations represented by 14 individuals. Meiotic abnormalities including bridges, fragments and univalents occurred in all individuals. At metaphase I, mean chromosome configuration of each cell was 2n = 10 = 0.36 I + 4.82 II. Most of the chromosomes were ring bivalents, but some were rod bivalents or univalents. Pairing index ranged from 71.04 to 77.76%. Chromosome bridges, fragments, unequal separation and lagging chromosomes were observed both at anaphase I and telophase I. All individuals produced bridges/fragments (10.37% of PMCs on average) at anaphase I, which suggested that they were all heterozygotes for paracentric inversions. However, there were some variations among individuals in frequency of bridge occurrence and size of fragments, which indicated that many different inversions existed in this subspecies. Further evidence is needed to answer why the structural heterozygosity exists so widely in the subspecies, and whether there is a relationship between this structural heterozygosity and ecological adaptation.

Correlation between geography and cytogenetic diversity in Pomegranate (Punica granatum L.) cultivars in Iran

Pomegranate (Punica granatum L.) is an important horticultural plant with several cultivated forms planted in different regions of Iran. Due to its economic importance, studies have been carried out to illustrate the genetic diversity at the chromosomal and molecular levels in different pomegranate cultivars growing in this region. This study analyzed chromosome pairing and B-chromosomes of 21 pomegranate cultivars and tried to investigate the effects of geographical parameters like altitude and longitude as well as elevation and the mean annual rainfall on cytogenetic diversity of these taxa. An ANOVA test revealed the presence of a significant difference for chiasmata and chromosome pairing among the cultivars, indicating their genetic differences. A positive significant correlation was observed between total chiasma frequency and terminal chiasmata, intercalary chiasmata and the mean number of quadrivalents. A significant positive correlation was observed between annual rainfall and the mean number of rod bivalents, while a significant negative correlation was found for the number of ring bivalents. Altitude did not show any correlation with the cytogenetic characters studied, but showed a significant negative correlation with the number of univalents. Longitude showed significant positive correlation with the number of ring bivalents and a negative correlation with the number of univalents and intercalary chiasmata. PCA analysis showed that both geographical and cytological features contribute greatly in the diversity observed in the pomegranate cultivars. The occurrence of multipolar cells and unreduced pollen grains were observed in some of the cultivars.

Karyotype analysis and meiotic behaviors of Ducrosia anethifolia: The first case study

The medicinal plant Ducrosia anethifolia (DC) Boiss is an annual herb of the Apiaceae family. It originated from Iran and it is used to treat headache and backache in traditional medicine. Mitotic study and meiotic behavior of chromosomes are presented for the first time for D. anethifolia in this study. D. anethifolia possessed n = 11 (2n = 2x = 22) chromosome number forming mainly both rod and ring bivalents with some amount of quadrivalents and univalents. Karyotype analysis according to Stebbins categories, placed chromosomes of this plant in symmetric class of 2A, indicating a symmetric karyotype. The types of chromosomes were metacentric and submetacentric with one pair of satellite chromosomes. A variety of abnormal chromosomal behaviors including chromosomal stickiness, bridge, laggards, micronucleus, mass chromatin and early chromosome migrations were observed, albeit with low frequency. Tetrads with four equal-sized cells were considered normal and any deviation as abnormal. Stain-ability of pollens as an estimation of their fertility was ninety-seven percent. In this study we had few meiotic abnormalities and, as a consequence, a high pollen fertility. Well-filled pollen grains with stained nuclei were regarded as apparently fertile while shriveled, smaller microspores and unstained pollen were counted as sterile. The study reveals that meiosis in this species is normal, with high meiotic index and regular bivalent formation in most studied cells. Key words: Ducrosia anethifolia, karyotype, meiosis, pollen fertility.

Connection between rod bivalents and incomplete meiotic association at NORs in Hordeum marinum Huds.

The hypothesis of a connection between rod bivalent formation and incomplete meiotic association at NORs of SAT-chromosomes of H. marinum is supported. PMCs of H. marinum ssp. gussoneanum (2x), two diploid ssp. marinum × ssp. gussoneanum (2x) hybrids and two ssp. gussoneanum (4x) × Secale cereale hybrids at metaphase I (M-I) were analyzed by in situ hybridization. The probe pTa71 labelled rDNA sites at NORs of a single pair of homologous or near-homologous SAT-chromosomes of H. marinum in each material. In the three diploids, M-I was regular with ring bivalents and one or a few rods (av.13.52 bound arms cell(-1)). More rod bivalents than the expected one out of seven, i.e. 30, 67 and 89% included rDNA-carrying chromosomes. Corresponding bound short arm frequencies were 0.89, 0.72 and 0.52, while long arms and arms of other chromosomes presented complete or near- complete association. The two heterogenomic hybrids had a less regular M-I (av. 8.04 bound arms cell(-1)) including 20% rDNA-carrying rods with bound arm frequencies of 0.29 in short and 0.87 in long arms. Positions of chromosome associations were established in all 150 rDNA-carrying bivalents. In 77 bivalents with short arm associations, 4% of these occurred proximally to, none at, and 96% distally to rDNA sites, i.e. in satellites. In 143 bivalents with long arm associations, 83% occurred at interstitial and 17% at terminal positions. The observations combine increased frequency of rDNA-carrying rods with decreased frequency of association at NOR regions of SAT-chromosomes. The basis for the relationship is discussed.

Together yes, but not coupled: new insights into the roles of RAD51 and DMC1 in plant meiotic recombination

The eukaryotic recombinases RAD51 and DMC1 are essential for DNA strand-exchange between homologous chromosomes during meiosis. RAD51 is also expressed during mitosis, and mediates homologous recombination (HR) between sister chromatids. It has been suggested that DMC1 might be involved in the switch from intersister chromatid recombination in somatic cells to interhomolog meiotic recombination. At meiosis, the Arabidopsis Atrad51 null mutant fails to synapse and has extensive chromosome fragmentation. The Atdmc1 null mutant is also asynaptic, but in this case chromosome fragmentation is absent. Thus in plants, AtDMC1 appears to be indispensable for interhomolog homologous recombination, whereas AtRAD51 seems to be more involved in intersister recombination. In this work, we have studied a new AtRAD51 knock-down mutant, Atrad51-2, which expresses only a small quantity of RAD51 protein. Atrad51-2 mutant plants are sterile and hypersensitive to DNA double-strand break induction, but their vegetative development is apparently normal. The meiotic phenotype of the mutant consists of partial synapsis, an elevated frequency of univalents, a low incidence of chromosome fragmentation and multivalent chromosome associations. Surprisingly, non-homologous chromosomes are involved in 51% of bivalents. The depletion of AtDMC1 in the Atrad51-2 background results in the loss of bivalents and in an increase of chromosome fragmentation. Our results suggest that a critical level of AtRAD51 is required to ensure the fidelity of HR during interchromosomal exchanges. Assuming the existence of asymmetrical DNA strand invasion during the initial steps of recombination, we have developed a working model in which the initial step of strand invasion is mediated by AtDMC1, with AtRAD51 required to check the fidelity of this process.

Looking for natural variation in chiasma frequency in Arabidopsis thaliana

Information concerning natural variation either in chiasma frequency or in the genetic basis of any such variation is a valuable tool to characterize phenotypic traits and their genetic control. Here meiotic recombination frequencies are analysed in nine geographically and ecologically diverse accessions of Arabidopsis thaliana, and a comparative study was carried out incorporating previous data from another eight accessions. Chiasma frequencies, estimated by counting rod and ring bivalents at metaphase I, varied up to 22% among accessions. However, no differences were found among plants of the same accession. There was a relationship, which does not necessarily imply direct proportionality, between the size of the chromosomes and their mean chiasma frequency. Chiasma frequency and distribution between arms and among chromosomes were not consistent over accessions. These findings indicate the existence of genetic factors controlling meiotic recombination both throughout the whole genome and at the whole chromosome level. The reliability of chiasma scoring as an indicator of reciprocal recombination events is also discussed.

Production and cytogenetics of trigeneric hybrid involving Triticum, Psathyrostachys and Secale

Trigeneric hybrids may help establish evolutionary relationships among different genomes present in the same cellular-genetic background, and also offers the possibility to transfer different alien characters into cultivated wheat. In this study, a new trigeneric hybrid involving species from the Triticum, Psathyrostachys and Secale was synthesized by crossing wheat-P. huashanica amphiploid (PHW-SA) with wheat-S. cereale amphiploid (Zhongsi 828). The crossability of F1 hybrid was high with 35.13%, and the fertility was 41.95%. The morphological characteristics of F1 plants resembled the parent Zhongsi 828. The trigeneric hybrids pollen mother cells (PMCs) regularly revealed averagely 19.88 univalents, 9.63 ring bivalents, 3.97 rod bivalents, 0.60 trivalents and 0.03 tetravalents per cell. Multivalents consisted of trivalents and tetravalents can be observed in 52.7% of cells. A variation of abnormal lagging chromosome, micronuclei and chromosome bridge were formed at anaphase I and telophase II. The mean chromosomes number of F2 progenies was 2n = 46.13, and the distribution range was 42–53. GISH results revealed that most F2 plants had 6–12 S. cereale chromosomes, and only 0–2 P. huashanica chromosomes were detected. The results indicated that S. cereale chromosomes can be preferentially transmitted in the F2 progenies of trigeneric hybrid than P. huashanica chromosomes. A survey of disease resistances revealed that the stripe rust resistance from the PHW-SA were completely expressed in the F1 and some F2 plants. The trigeneric hybrid could be a useful bridge for the transference of P. huashanica and S. cereale chromatins to common wheat.

Population Diversity and Polyploidy Incidence in 3 <i>Silene</i> Species. A Cytological Approach

Cytological studies were performed in 20 populations of 3 Silene species of the section Auriculatae L., Silene gynodiocia Ghazanfar, S. crispans Litw., S. indeprensa Schischk. The populations studied had 2n=2x=24, 2n=4x=48 and 2n=8x=96 chromosome number, showing 2 polyploidy levels for S. indeprensa and S. gynodiocia. The chromosomes were mostly metacentric and submetacentric but 1 pair of teloentric chromosome was observed in the octaploid Dargaz population of S. indeprensa. The ANOVA test showed no significant difference among populations of S. indeprensa and populations of S. gynodiocia for size of the chromosomes, mean chromosome length, A1 and A2 indices as well as TF value. This indicates that no significant chromatin loss or gain has occurred in the process of karyotype differentiation in these populations, and in the case of octaploid and tetraploid populations, still the mean value of chromosomes are maintained. However, the species differed significantly for CV value, indicating that during species diversification a change has occurred in the size of chromosomes within a karyotype due to structural changes of the chromosomes. Meiosis analysis showed that the chromosomes mainly form bivalents and univalents in the metaphase of meiosis I, although some amounts of quadrivalents were observed in all populations including diploids due to heterozygote translocations. T-test analysis showed significant difference in the relative values of total and terminal chiasmata as well as a number of ring bivalents between the populations having 2n=24 and 2n=48 chromosome number indicating that with an increase in polyploidy level, significant change has occurred in the number of genes controlling chiasma frequency. The occurrence of unreduced pollen grains indicates the role of this phenomenon in polyploidy incidence in the species studied.

Meiotic behaviour of chromosomes in three predator species of the subfamily Asopinae (Heteroptera: Pentatomidae)

The study of chromosome behaviour has been carried out on males of three species of the Asopinae (Pentatomidae) bugs Andrallus spinidens (Fabricius, 1787), Canthecona furcellata Wolff, 1801 and Perillus bioculatus (Fabricius, 1775) collected in India. All the species have XY sex chromosome system and 12 autosomes (2n=14=12A+XY). The general course of meiosis is fairly uniform and is typical for heteropteran species. However, the species differ in the extent of decondensation of the autosomes during the diffuse stage and the number of ring bivalents at diplotene/ diakinesis. Also, a metaphase I arrangement of chromosomes which is different from the typical Pentatomidae type has been observed in C. furcellata and P. bioculatus.

Microsporogenesis in three wild species of the genusAntirrhinumL. (A. litigiosumPau,A. pulverulenthumLazaro andA. subbaeticumGüemes, Sánchez and Mateu)

The diploid chromosome number (2n = 2x = 16) in three wild species A. litigiosum Pau, A. pul- verulenthum Lazaro and A. subbaeticum Guemes, Sanchez & Mateu, belonging to the genus Antirrhinum was cytologically observed. Genetic stability of the simultaneous meiotic division type was found in these natural growing snapdragons. The synchronicity at the initial meiotic stages and at tetrad and pollen creation was high and disappeared with the diakinesis initiation. Refl ecting the systematic position of the studied species into Antirrhinum, the performed investigation mani- fested similarity: in the presence of univalents and quadrivalent confi gurations parallel with bivalents at the early meiotic stages; in the type of disturbances at metaphase and anaphase stages; in the tetrad formation and pollen characteristics; in the particularity of the tapetal cell division. There were dissimilarities in the bivalent chiasma formation and localisation and in the level of the meiotic dis- orders. Seven different chromosome associations were observed at diakinesis and metaphase one in A. pulveru- lenthum PMCs, while in the other two Antirrhinum species they ranged between 12 and 13. The highest value of ring bivalents, total and mean chiasma number per bivalent, was found in A. pulverulenthum PMCs, while the lowest value of these characteristics was evaluated in the A. litigiosum cells. The chromosome behaviour during anaphase stages showed more changes in A. subbaeticum PMCs and the most regularity in the A. pul- verulenthum cells, which were refl ected in the value of the pollen fertility (83.7% and 98.4% respectively). The established specify and differences demonstrated genetic diversity between A. litigiosum, A. pulverulenthum and A. subbaeticum genomes.

Studies on cytotoxicity induced by DES and SA in Vicia faba var. major

The effect of diethyl sulphate (DES) and sodium azide (SA) was studied on the meiotic behaviour of Vicia faba L. var. major in the M1 generation. Five concentrations of SA (0.01%, 0.02%, 0.03%, 0.04%, and 0.05%) were combined with DES (0.02%) to study the synergistic and antagonistic effects of these 2 mutagens. A dose-dependent increase in chromosomal aberrations was recorded in populations treated with both the mutagens individually and their combination doses. The main chromosomal aberrations were stickiness, precocious separations, univalents, multivalents, laggards, unequal separations of chromosomes, micronuclei, disturbed polarity, multinucleate condition, and cytomixis. The stickiness and stray bivalents at metaphase I/II, bridges with or without fragments at anaphase I/II, disturbed polarity, and cytomixis at telophase I/II were the dominant anomalies. The univalents, rod bivalents, and multivalents showed dose-dependent increases, whereas the ring bivalents and chiasma frequency per cell showed dose-dependent decreases both in single as well as in combined mutagenic treatments as compared to the control.

Meiotic Behavior of Wild, Synthetic and Cultivated Wheats

Wild relatives of bread wheat are potential sources of valuable genetic materials for wheat improvement. Genomic relationship and cross-ability between plant species can be deduced from chromosomal structure, size and behavior during meiotic division. In this study, the meiotic behavior of 21 wheat genotypes possessing the 3 ploidy levels of diploid, tetraploid and hexaploid and belonging to 3 wild, cultivated and synthetic growing statuses was investigated. The results indicated that the average number of ring bivalents at metaphase I ranged from 60 to 100% in the studied genotypes with the lowest rate belonging to the diploid wild relative wheat species. Four meiotic abnormalities including (1) precocious chromosome migration to the poles at metaphase I, (2) laggard chromosomes at anaphase I and telophase I, (3) chromosome stickiness and chromosome bridge at anaphase I and (4) formation of micronuclei at telophase I and in the tetrad cells were found in the studied genotypes. The highest meiotic abnormalities were found in synthetic wheat accessions. The average value of the meiotic index for the studied wheat genotypes was above 99%, revealing their normal meiotic behavior.