Meiotic Irregularities Research Articles

Maternal age-related differential global expression profiles observed in human oocytes

The age-related decline in female fertility has been attributed to a variety of causes including progressive oocyte depletion, meiotic irregularities and mitochondrial dysfunction. However, additional factors could potentially be involved. To explore this possibility, comprehensive analysis of gene expression in human oocytes, discarded following IVF procedures and segregated by age, was undertaken using microarray methods. These findings indicate that the expression of oocyte genes, in a variety of major functional categories including cell cycle regulation, cytoskeletal structure, energy pathways, transcription control, and stress responses, are influenced by maternal age. These results are corroborated by a complementary extensive study using mouse oocytes.

Cytomixis impairs meiosis and influences reproductive success inChlorophytum comosum (Thunb) Jacq. — An additional strategy and possible implications

Spontaneous intercellular chromatin migration/cytomixis was observed to occur in the pollen mother cells (PMCs) of the Chlorophytum comosum for the first time. The migration through cytomictic channels was more pronounced in meiosis-I and very rare in meiosis-II. The process was associated with erratic meiosis, which was characterized by defects in chromosome organization and segregation. Cytomixis was more intense in the month of April than in July and consequently the frequency of meiotic irregularities was much more pronounced during the month of April. As a consequence of abnormal meiosis, fertility was drastically reduced resulting in meager seed efficiency of 17% only. Recombination system also does not guarantee the release of sufficient variability. We view the phenomenon of cytomixis as genetically controlled mechanism involving meiotic genes and operating through signal transduction pathway triggered by the environmental stimuli. The evolutionary significance and tenable hypothesis in the backdrop of existing literature is also proposed.

Cytological microevolutive changes in hexaploid triticale (X Triticosecale Wittmack)

The objectives of this study were to evaluate a) the success in meiosis of disruptively selected triticale progenies used as recurrent selection parents, and b) the changes that took place in their meiotic behavior after three cycles of recurrent selection in hexaploid triticale. From samples of five immature spikes per experimental unit, the meiotic index (MI) and the percentage of tetrads containing micronuclei in 1, 2, 3 or 4 microspores were estimated. The families used as recurrent selection parents showed a significantly higher MI than those with the lower agronomical performance. A positive and significant linear relation between the MI and cycles of recurrent selection was observed. The analysis of the tetrads with micronuclei showed a non-significant positive tendency to increase the percentage of tetrads with micronuclei in 1 microspore in the more evolved cycle, while negative linear relations between tetrads with micronuclei in 2, 3 and 4 microspores and cycles were observed. These results suggest that in triticale those individuals with superior reproductive performance tend to reduce their meiotic irregularities.

Meiotic Behavior of Carica papaya L.: Spontaneous Chromosome Instability and Elimination in Important cvs. in North Indian Conditions

Cytogenetical analysis was done in tropical species of papaya that is widely cultivated for its fruits and papain production. The proper and orderly chromosome behavior of the species is a perquisite to ensure high fertility and seed set in the crop. A study on pre-meiotic and post-meiotic stages was done on commercially important cultivars of India and few exotic cultivars. The meiosis in the flower buds was highly disturbed and many meiotic irregularities were recorded from the material fixed in summar. These ranged from chromosome stickiness (44%), chromatin bridges (21.1%), laggards (4.8), chromosome diminution/degeneration (5.2), and micronucleus (5.9%) formation, in the commercially important varieties. Pollen stickiness accounting for persistent pollen adherence in groups of 3–10 was observed in all the varieties ranging from 85.95% in cv. CO2 to 11.64% in CO5. Callose deposition on tetrads accounting for adhesion of pollen grains (permanent tetrads) was also observed. These were found to have a profound effect on the pollen fertility of the cultivars, wherein most of the commercial papaya cultivars had less than 50% of fertile pollen. Thus the role of meiotic irregularities in poor seed setting and seed production capacities under northern Indian conditions, specifically during the summer season has been established. Genetic or abiotic stress factors could be responsible for inducing such kind of anomalies, which are manifested in the form of pollen sterility and poor seed setting. Crop regulation strategies need to be evolved, so that the maximum seed set and fruit production occurs after this period to off set the restrictions imposed due to irregular meiosis.

Characterization of the Species Epidendrum cinnabarium Salzm. (Epidendroideae: Orchidaceae) Occurring in Dunas Do Abaete-Salvador, Ba-Brasil

This work has as its purpose to analyze the Epidendrum cinnabarium species, which can be found within the “Environment Protection Area of Abaete Lakes and Dunes” (“Area de Protecao Ambiental das Lagoas e Dunas de Abaete”)-APA/Abaete, Salvador, Bahia State-Brazil. As for the cytogenetic aspects it aims at determining the chromosome number, on the ploidy level, the types of interphasic nuclei, and at evaluating the possible meiotic irregularities of this species. In the mitotic analysis, radicular meristem has been pre-treated with 8-hydroxyquinoline and colored with aid of the Feulgen method. In order to carry out the meiotic analysis, microsporocytes were prepared by squashing and staining with 0.2% propionic carmine. The results showed 2n>240, suggesting the occurrence of poliploidy, an interphasic nucleus of the semi-reticulate type with the presence of chromocenters displaying a variable number, besides an irregular meiotic behavior, with the presence of laggard chromosomes and laggard chromatids, as well eventually anaphasic bridges and a low percentage of abnormal tetrads.

Chromosome numbers and meiotic behavior of some Paspalum accessions

Chromosome number and meiotic behavior were evaluated in 36 Brazilian accessions of the grass Paspalum (which had never previously been analyzed) to determinate which accessions might be useful in interspecific hybridizations. The analysis showed that one accession of Paspalum coryphaeum was diploid (2n = 2x = 20) and one accession of Paspalum conspersum hexaploid (2n = 6x = 60), the remaining 34 accessions being tetraploid (2n = 4x = 40). The pairing configuration was typical for the ploidy level i.e. in the diploid, chromosomes paired as 10 bivalents, in tetraploids as bi-, tri- and quadrivalents, and in hexaploid as 30 bivalents. A low frequency of meiotic abnormalities (less than 10%) was observed in the diploid, hexaploid and some tetraploid accessions, although the majority of tetraploid accessions showed a high frequency of meiotic irregularities. The use of accessions with a low frequency of meiotic abnormalities in breeding programs is discussed.

A Comparative Cytogenetic Analysis between the Grasshopper Species Chromacris nuptialis and C. speciosa (Romaleidae): Constitutive Heterochromatin Variability and rDNA Sites

The chromosomes of Chromacris nuptialis and C. speciosa were comparatively analyzed using different cytogenetic techniques, in order to determine the level of karyotypic similarities and differences between the species. The results show similarities in chromosome number (2n=23,X0) and acrocentric morphology. In some C. nuptialis individuals meiotic irregularities were detected involving the L(2) bivalent. This bivalent was delayed and presented anaphasic bridges and other aberrations. Differences in constitutive heterochromatin (CH) patterns and composition were observed through C-banding and fluorochromes staining. Silver nitrate staining revealed a single medium nucleolar organizer regions (NORs) pair, per species. Differences were also observed in NORs location, which was pericentromeric in C. nuptialis and proximal in C. speciosa. FISH using an rDNA probe confirmed the existence of ribosomal sites coinciding with active regions visualized by silver nitrate. The possible implications of the karyotype differences observed between both species are discussed.

Mitotic karyotype stability and meiotic irregularities in the families Loranthaceae Juss. and Viscaceae Miq

Chromosome number, interphase nuclear structure, prophase chromosome condensation patterns, and meiotic behaviour were analysed in 14 Brazilian species within the families Loranthaceae and Viscacea...

Cytological abnormalities in Artemisia pallens Wall. induced by gamma rays

The effect of gamma rays on Artemisia pallens Wall. have been studied with reference to behaviour of chromosomes and frequency of cytological abnormalities. Various mitotic and meiotic irregularities were studied in m1 plants raised from seeds of A. pallens treated with gamma rays at various doses like 150, 200, 250, 300, 350, 400 and 500 gy. gamma rays caused a dose dependent increase and decrease in mitotic inhibition and mitotic index respectively. From these treatments, a significant percentage of chromosomal abnormalities such as formation of univalents, fragments, stickiness, chromatin bridges with or without laggards were induced. The total percentage of cells with chromosomal aberrations increased with increase in dose.

Aberrant Meiotic Divisions in a Hordeum lechleri×H. vulgare Hybrid

Five plants produced in a H. lechleri×H. vulgare cross comprised four trihaploids of H. lechleri with 2n = 21 and one aneuploid interspecific hybrid with 2n = 25–26. Somatic cells of the hybrid lacked H. vulgare chromosomes nos 1 and 6 and one, or two H. lechleri chromosomes, but had two representatives of H. vulgare chromosome no. 7. Chromosome numbers of meiotic metaphases ranged from 4 to 54 with peaks at or just below euploid numbers corresponding to the prevalent aneuploid chromosome number of the hybrid. The cause of chromosome numbers at and around 2n = 14 and 2n = 7 is proposed to be intraspecific, intergenomic elimination of one and two H. lechleri genomes, respectively, in addition to the elimination of all H. vulgare chromosomes. It is suggested that intraspecific, intergenomic elimination occurs in allopolyploids in nature, thereby causing reduction in chromosome number within species. Numbers above 2n = 29 are ascribed to spontaneous chromosome doubling. Meiotic irregularities such as misdivisions, “budding”, telocentrics, fragmentation of the whole chromosome set, and non-synchronized divisions were common. The production of “buds”, generally with few chromosomes, may have added to the variability in chromosome numbers.

Cytogenetic Studies in Ethiopian Landraces of Tetraploid Wheat (Tviticum Turgidum L.). II. Spontaneous Chromosome Translocations and Fertility

Meiosis was studied in seven tetraploid (2n =4x = 28) wheat (Triticum turgidum L.) landrace morphotypes of Ethiopian origin and one introduced durum variety, ‘Boohai’. The objectives were to detect the presence of chromosome structural rearrangements by using the variety ‘Senatore Cappelli’ (SC) as a reference and to investigate if the previously reported low fertility (seed set) of the landraces has a chromosomal basis. All the parents exhibited a normal bivalent pairing at metaphase I (MI) except one (CD-7) that showed a relatively high proportion of pollen mother cells (PMC) with univalents (0.40/PMC). ‘Boohai’ and two of the landraces from Ambo district were structurally similar to SC. The remaining five landraces each differed by one translocation from SC. These, in turn, differed from each other by one or two translocations while two of the landraces carried the same translocation. However, in some of the landrace x landrace hybrids there was a tendency of restricting the formation of more than one quadrivalent per PMC. Four different translocations involving four to six chromosomes are present in the material studied. Lack of pairing, as measured by univalent frequency, vaned for the different F, hybrids. Generally, however, it was lower in the F, hybrids between the landraces than in hybrids between the landraces and SC. In almost all cases, division stages following MI proceeded as normal. Inversions were absent or too small to be detected. Meiotic irregularities have little to do with the low fertility of most of the parental landraces. In the F, hybrids, on the other hand, high univalent frequency and multivalent associations impaired seed set depending upon the cross combination. The results indicate that chromosome structural Polymorphism for translocations may be common in Ethiopian tetraploid wheat landraces that might have played a role in maintaining their diversity by producing new linkage relationships. From breeding perspective, the bulk selection method and/or backcrossing to high fertility genotypes seem to be appropriate when these landraces are employed in hybridization programmes.

Differentiation of the S<sub>t</sub>Y genomes in <i>Elymus</i> species as referred by meiotic pairing in interspecific hybrids and its evolutionary significance

Hybridization-differentiation is a major pathway of speciation and the active force of plant evolution, including homoploid speciation without change of chromosome numbers. Effective isolation between parental species and their hybrid derivatives plays an essential role in homoploid speciation for stabilizing a newly formed species. Studies of isolation mechanisms will facilitate our understanding of the speciation process. The genus Elymus of Triticeae ( Poaceae) includes ca. 150 polyploid species with different genomes, viz. the StH, St Y , StHY, StPY, and StWY from different origins, providing an ideal group for studying mechanisms of polyploid and homoploid speciation. There are about 30 tetraploid species containing the StY genomes distributed in temperate Asia and the eastern margin of Europe. In order to study genomic relationships of the StY Elymus species, samples representing 26 species collected from Western through Eastern Asia were extensively hybridized with each other. Meiotic pairing at metaphase-I of the intra- and interspecific hybrids was analyzed, which revealed a significant differentiation pattern in hornology of the StY genomes among Elymus species studied. Species from the same regions, e. g. within eastern or western Asia, shared the StY genomes with a relatively low level of differentiation, but species from different regions, e. g. between eastern and western Asia, shared substantially differentiated StY genomes. Species from Central Asia contained intermediately differentiated StY genomes compared with those from western and eastern Asia. The discovery of geographical differentiation of the StY genomes in tetraploid Elymus species has significance for study of evolutionary processes and mechanisms of homoploid speciation in Elymus. In addition to other well-recognized factors responsible for the isolation between parental species and their hybrid derivatives during the hybridization-differentiation process ( such as temporal, spatial, genie , and ecological isolation) , the authors believe that meiotic irregularity caused by genomic differentiation between species also provides an important mechanism for homoploid speciation.

Relationships between Meiotic Irregularities and Fertility in Diploid and Triploid Musa L.

Most of the widely grown banana cultivars are triploids (2n=3x=33). They are characterized by low male and female fertility and/or complete male and female sterility. On the contrary, diploids are generally both male and female fertile. Banana improvement programs use interploidy crosses to introgress useful genes from wild or improved diploids to triploid landraces. This study investigated the effects of meiotic irregularities on the fertility of diploid and triploid Musa accessions. Our results showed that precocious chromosomes movements, lagging chromosomes and univalents were observed in most of the accessions. In general, a higher incidence of univalent formation was related to low pollen fertility and polyspore formation.

Meiotic Abnormalities and Tetraploidy (by Lead Nitrate) Induced by Heavy Metals (Pb, Cu, Hg, Zn) Helianthus annuus L.

Cytological effects of some (Pb, Cu, Zn, Hg) heavy metals were tested on meiotic studies of Helianthus annuus. The used heavy metals did not show much variations in the type of induced abnormal PMCs. The abundant meiotic irregularities stickiness, lagging, bridges, unequal separation, fragmentation etc. were observed. Mercury was the most toxic of all used heavy metals since it produced highest percentage of abnormal PMCs. Lead nitrate is a mutagen which induce tetraploidy.

Cytogenetic Studies of Some F1 Hybrids between Wild and Cultivated Taxa of Capsicum L.

Two F1 hybrids one between wild C. annuum var glabrisculum and C. frutescens (H1) and another between wild C. annuum var antigua and C. frutescens (H2) were obtained. Cytogenetic analysis of F1 hybrids showed that the parental genomes differ from each other by 2 or 1 translocations, 1 inversion and some minor structural alterations leading to reduced homologies between the respective parental genomes. Meiotic irregularities pollen and seed sterilities were higher in H2 than in H1. Probable reasons for the differences in respect of their crossability relationships, chromosome pairing and fertilities in non-rearing of reciprocal hybrids are suggested. The role of chromosome structural changes in genome differentiation is suggested. Isolating mechanisms viz., hybrid inviability and hybrid weakness in the reciprocal cross and hybrid sterility in the F1 hybrids are in operation.

Introgression de la résistance à la cécidomyie chez le Blé par croisement avec une souche d'Aegilops ventricosa marocaine

The introduction of alien genetic material through interspecific or intergeneric hybridisation allowed the transfer of resistant genes to many diseases and pests. The Hessian fly Mayetiola destructor is one of the most destructive pests of wheat crops. The Ae. ventricosa is one of the most important sources of alien variation for wheat breeding. For transferring resistance to wheat, interspecific crosses were conducted between Ae. ventricosa resistant accessions with both bread and durum wheat. The low viability and the sterility of the interspecific hybrids F1 and its progenies have a determinant impact on seed set and number of hybrid plants produced. Meiotic analyses showed meiotic irregularities, which are probably causing sterility in the interspecific progenies. Most interspecific offspring maintained were resistant to the Hessian fly. In the fourth generation, some were still showing segregation of the resistance. In the fifth generation, all the progenies analysed were however resistant at 100%.

Chromosome studies in Andean taxa of Alstroemeria (Alstroemeriaceae)

Meiotic or mitotic chromosomes of seven Alstroemeria taxa, native in Argentina and Chile and with Andean distribution were studied: A. andina ssp. venustula, A. hookeri ssp. cummingiana, A. hookeri ssp. recumbens, A. pallida, A. patagonica, A. pseudospathulata and A. pygmaea. All were diploid with 2n = 16. Karyotypes of A. andina ssp. venustula and A. pygmaea were analysed, revealing similarity to previously analysed species. Thus, to all existing arguments for not retaining Schickendantzia as a separate genus, we can add another one which merges A. pygmaea with other Alstroemeria species, and does not support its taxonomic uniqueness. In general, the meiotic behaviour was normal, with regular formation of eight bivalents except in A. hookeri ssp. cummingiana, in one plant of which meiotic irregularities at various stages were observed. At the tetrad stage a large percentage of the cells presented micronuclei. The presence of 0–2 supernumerary chromosomes in A. hookeri ssp. recumbens is recorded. The karyotype asymmetry presented by most Alstroemeria species is discussed. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 138, 451–459.

Chromosome contribution to Andean Polyploid Species of Senecio (Asteraceae), from Argentina

Abstract Meiotic chromosome numbers were determined and observations of meiotic behavior were made in six species and two hybrid specimens of Senecio L. (Asteraceae). Two different numbers were found: 2n=4x=40 in S. pogonias Cabr., S. ragonesei Cabr., S. sectilis Griseb. and S. viridis Phil. var. radiatus R. E. Fr. and 2n=8x=80 in S. subulatus D. Don. var. subulatus and in S. uspallatensis Hook. et Arn.; the latter showed the same chromosome number previously reported. The chromosome number of the hybrid individuals was 2n=4x=40, being their putative parents S. ragonesei and S. sectilis. B chromosomes were found in some individuals of S. pogonias, S. sectilis, S. subulatus var. subulatus and S. uspallatensis. Many meiotic irregularities such as bridges, fragments, laggard chromosomes, micronuclei and cellular fusion were observed. The results are analyzed in relation to the persistence and success of these polyploids, and the speciation mechanisms operating within this group are discussed.

Meiotic Behavior and Chromosome Number of Four Natural Populations of Peperina [Minthostachys mollis (Kunth.) Griseb.

The meiotic behavior and somatic chromosomic number of 4 populations belonging to Minthostachys mollis (Kunth.) Griseb. species were determined. This is the first study on these aspects not only for this species but also for the entire Minthostachys genus. The most frequent meiotic irregularities observed were univalents, laggards and triads; whereas cytomixis and bridges were observed only in 2 populations. Besides the occurrence of triads, the presence of hexads and dyads were also seen. With respect to the somatic chromosomic number, this study reveals the presence of 2n=42 chromosomes for the P 1 , P 2 and P 3 populations and 2n=24 chromosomes for the P 4 population.

Aberrant meiotic behavior in Agave tequilana Weber var. azul

BackgroundAgave tequilana Weber var. azul, is the only one variety permitted by federal law in México to be used for tequila production which is the most popular contemporary alcoholic beverage made from agave and recognized worldwide. Despite the economic, genetic, and ornamental value of the plant, it has not been subjected to detailed cytogenetic research, which could lead to a better understanding of its reproduction for future genetic improvement.The objective of this work was to study the meiotic behavior in pollen mother cells and its implications on the pollen viability in Agave tequilana Weber var. azul.ResultsThe analysis of Pollen Mother Cells in anaphase I (A-I) showed 82.56% of cells with a normal anaphase and, 17.44% with an irregular anaphase. In which 5.28% corresponded to cells with side arm bridges (SAB); 3.68% cells with one bridge and one fragment; 2.58% of irregular anaphase showed cells with one or two lagging chromosomes and 2.95% showed one acentric fragment; cells with two bridges and cells with two bridges and one acentric fragment were observed in frequencies of 1.60% and 1.35% respectively. In anaphase II some cells showed bridges and fragments too. Aberrant A-I cells had many shrunken or empty pollen grains (42.00%) and 58.00 % viable pollen.ConclusionThe observed meiotic irregularities suggest that structural chromosome aberrations have occurred, such as heterozygous inversions, sister chromatid exchanges, deletions and duplications which in turn are reflected in a low pollen viability.