Meiotic Chromosome Behavior Research Articles

Hypersensitivity of primordial germ cells to compromised replication-associated DNA repair involves ATM-p53-p21 signaling.

Genome maintenance in germ cells is critical for fertility and the stable propagation of species. While mechanisms of meiotic DNA repair and chromosome behavior are well-characterized, the same is not true for primordial germ cells (PGCs), which arise and propagate during very early stages of mammalian development. Fanconi anemia (FA), a genomic instability syndrome that includes hypogonadism and testicular failure phenotypes, is caused by mutations in genes encoding a complex of proteins involved in repair of DNA lesions associated with DNA replication. The signaling mechanisms underlying hypogonadism and testicular failure in FA patients or mouse models are unknown. We conducted genetic studies to show that hypogonadism of Fancm mutant mice is a result of reduced proliferation, but not apoptosis, of PGCs, resulting in reduced germ cells in neonates of both sexes. Progressive loss of germ cells in adult males also occurs, overlaid with an elevated level of meiotic DNA damage. Genetic studies indicated that ATM-p53-p21 signaling is partially responsible for the germ cell deficiency.

New Plant Type Mutants in Jute (Corchorus olitorius L.)

Three macromutants namely, 'pigmented stem', 'viridis' and 'lax branching', of jute (Corchorus olitorius L. - JRO 524; commercial fibre yielding crop) were induced at M2 following gamma irradiations and EMS (Ethyl Methane Sulphonate) treatments. The true breeding mutants (selfed seeds of a single phenotypically stable plant forwarded in each generation from M4) are assessed considering different attributes like germination, survivability, meiotic chromosome behavior, pollen fertility and viability and quantitative traits across the generations (M5, M6 and M7) in relation to control under a uniform field condition(s). Further, genetic variations between/among the mutants and between mutant(s) and control is also analyzed from seed protein (SDS-PAGE - sodium dodecyl sulphate-polyacrylamide gel electrophoresis), RAPD (Random Amplification of Polymorphic DNA) and ISSR (inter-simple sequence repeat) profiles. Pigment profiles following TLC (Thin Layer Chromatography) have been studied in 'viridis' and control. Inheritance of the mutant trait(s) has also been assessed from reciprocal crossings performed between control and mutants. Results suggest that the mutants are true breeding, stable and significant and may enrich genetic resources in the species.

Arabidopsis PTD Is Required for Type I Crossover Formation and Affects Recombination Frequency in Two Different Chromosomal Regions

In eukaryotes, crossovers together with sister chromatid cohesion maintain physical association between homologous chromosomes, ensuring accurate chromosome segregation during meiosis I and resulting in exchange of genetic information between homologues. The Arabidopsis PTD (Parting Dancers) gene affects the level of meiotic crossover formation, but its functional relationships with other core meiotic genes, such as AtSPO11-1, AtRAD51, and AtMSH4, are unclear; whether PTD has other functions in meiosis is also unknown. To further analyze PTD function and to test for epistatic relationships, we compared the meiotic chromosome behaviors of Atspo11-1 ptd and Atrad51 ptd double mutants with the relevant single mutants. The results suggest that PTD functions downstream of AtSPO11-1 and AtRAD51 in the meiotic recombination pathway. Furthermore, we found that meiotic defects in rck ptd and Atmsh4 ptd double mutants showed similar meiotic phenotypes to those of the relevant single mutants, providing genetic evidences for roles of PTD and RCK in the type I crossovers pathway. Moreover, we employed a pollen tetrad-based fluorescence method and found that the meiotic crossover frequencies in two genetic intervals were significantly reduced from 6.63% and 22.26% in wild-type to 1.14% and 6.36%, respectively, in the ptd-2 mutant. These results revealed new aspects of PTD function in meiotic crossover formation.

Triploid planarian reproduces truly bisexually with euploid gametes produced through a different meiotic system between sex

Although polyploids are common among plants and some animals, polyploidization often causes reproductive failure. Triploids, in particular, are characterized by the problems of chromosomal pairing and segregation during meiosis, which may cause aneuploid gametes and results in sterility. Thus, they are generally considered to reproduce only asexually. In the case of the Platyhelminthes Dugesia ryukyuensis, populations with triploid karyotypes are normally found in nature as both fissiparous and oviparous triploids. Fissiparous triploids can also be experimentally sexualized if they are fed sexual planarians, developing both gonads and other reproductive organs. Fully sexualized worms begin reproducing by copulation rather than fission. In this study, we examined the genotypes of the offspring obtained by breeding sexualized triploids and found that the offspring inherited genes from both parents, i.e., they reproduced truly bisexually. Furthermore, meiotic chromosome behavior in triploid sexualized planarians differed significantly between male and female germ lines, in that female germ line cells remained triploid until prophase I, whereas male germ line cells appeared to become diploid before entry into meiosis. Oocytes at the late diplotene stage contained not only paired bivalents but also unpaired univalents that were suggested to produce diploid eggs if they remained in subsequent processes. Triploid planarians may therefore form euploid gametes by different meiotic systems in female and male germ lines and thus are be able to reproduce sexually in contrast to many other triploid organisms.

Cytological and karyological observations on two endemic giant pill-millipedesArthrosphaera(Pocock 1895) (Diplopoda: Sphaerotheriida) of the Western Ghats of India

Cytological features and karyomorphology of two endemic giant pill-millipedes (Arthrosphaera fumosa and A. magna) of the Western Ghats were studied based on the meiotic cell divisions using Giemsa staining technique. Different meiotic stages of spermatogonial cell divisions were compared and karyotypes were constructed from the metaphase stages. The diploid chromosome number, 2n = 30, in A. fumosa as well as A. magna with XY sex determination system was seen. Most of the meiotic chromosome behaviors were similar between the millipede species. All meiotic chromosomes in A. fumosa belonged to acrocentric type, while in A. magna 27 were acrocentrics, two (3rd and 10th) were sub-metacentrics and one (5th) was metacentric. The relative lengths of autosomes in A. fumosa and A. magna were 21.9–109.3 and 38.8–90.6, respectively. The X chromosome was longer than the Y chromosome in both millipedes. The relative lengths of the X chromosomes of A. fumosa and A. magna were 130.1 and 103.6, while for the Y chromosome ...

Meiotic chromosome pairing behaviour of natural tetraploids and induced autotetraploids of Actinidia chinensis

Non-preferential chromosome pairing was identified in tetraploid Actinidia chinensis and a higher mean multivalent frequency in pollen mother cells was found in colchine-induced tetraploids of A. chinensis compared with naturally occurring tetraploids. Diploid and tetraploid Actinidia chinensis are used for the development of kiwifruit cultivars. Diploid germplasm can be exploited in a tetraploid breeding programme via unreduced (2n) gametes and chemical-induced chromosome doubling of diploid cultivars and selections. Meiotic chromosome behaviour in diploid A. chinensis 'Hort16A' and colchicine-induced tetraploids from 'Hort16A' was analysed and compared with that in a diploid male and tetraploid males of A. chinensis raised from seeds sourced from the wild in China. Both naturally occurring and induced tetraploids formed multivalents, but colchicine-induced tetraploids showed a higher mean multivalent frequency in the pollen mother cells. Lagging chromosomes at anaphase I and II were observed at low frequencies in the colchicine-induced tetraploids. To investigate whether preferential or non-preferential chromosome pairing occurs in tetraploid A. chinensis, the inheritance of microsatellite alleles was analysed in the tetraploid progeny of crosses between A. chinensis (4x) and A. arguta (4x). The frequencies of inherited microsatellite allelic combinations in the hybrids suggested that non-preferential chromosome pairing had occurred in the tetraploid A. chinensis parent.

Chromosome studies on two endemic pill-millipedes of the genus Arthrosphaera (Diplopoda: Sphaerotheriida) from the Western Ghats of India

The diploid chromosome number of pill-millipedes (Class, Diplopoda) varies between 16 (Glomeridae) and 30 (Arthrosphaeridae) with XY pattern of sex determination. The meiotic division stages and karyotype of chromosomes derived from the spermatogonial metaphase of two pill-millipedes Arthrosphaera craspedota and A. lutescens of the Western Ghats of India revealed the diploid chromosome number 30 and 26, respectively. The meiotic chromosome behavior was almost similar in these species. The zygotene in A. craspedota consists of bouquet formation, the diplotene bivalents exhibited characteristic fuzziness and the sex bivalents were conspicuous with terminal chiasma. Deeply stained heterochromatin regions in chromosomes and conspicuous sex bivalents were seen in A. lutescens. Autosomes as well as sex chromosomes were acrocentric with relative length range was 20.6–170.1 in A. craspedota, while 27.6–145.2 in A. lutescens. It is believed that the acrocentric nature of chromosomes in Arthrosphaera was the result of Robertsonian changes, pericentric inversions and polyploidy. Recent studies revealed that the Malagasy-Indian genus Arthrosphaera evolved between 160 and 80 mya (breakup of Madagascar and India). Cytological investigations on endemic Arthrosphaera (A. brandtii) and its sister taxon Sphaeromimus distributed in the Madagascar may provide more insight on the chromosomal evolutionary pattern in pill-millipedes.

High frequency microcloning of Aloe vera and their true-to-type conformity by molecular cytogenetic assessment of two years old field growing regenerated plants.

BackgroundAloe vera (L.) Burm.f is an important industrial crop, which has enormous application in pharmaceutical, cosmetic and food industries. Thereby, the demand for quality planting material of A. vera is increasing worldwide. Micropropagation is the widely accepted practical application of plant biotechnology that has gained the status of a multibillion-dollar industry throughout the world and this techniques can be used to meet the industrial demand of A. vera. Present studies aim to develop a proficient methods of high-frequency true-to-type plantlet regeneration without intermediate callus phase for A. vera.ResultsNodal portion of rhizomatous stem of A. vera were cultured on Murashige and Skoog (MS) medium (Physiol. Plant. 15:473 – 497, 1962) supplemented with various cytokinin and A. vera leaf gel (AvG) as organic supplement. Number of proliferated shoots per explant was increased along with the regeneration cycles and on MS medium supplemented with 2.5 mg/L 6-benzylaminopurine and 10.0% (v/v) AvG, only 17.8 ± 0.35 shoots per explant were induced on 1st regeneration cycle whereas on 3rd regeneration cycle these number increase to 38.5 ± 0.44 shoots per explant on the same medium composition. AvG have an encouraging role to increase the proliferation rate and on 3rd regeneration cycle 27.6 ± 0.53 shoot per explant induced on 2.5 mg/L BAP, but these number increase to 38.5 ± 0.44 shoots per explant when 10.0% (v/v) AvG was added along with 2.5 mg/L BAP. After transfer of individual excised shoots to a one-third strength MS medium containing 20.0% (v/v) AvG, all the shoots formed whole plantlets with maximum number (9.6 ± 0.29) of roots per shoot. 95.0% of the regenerated plantlets survived on poly-green house. Normal flower appeared in 84.2% field growing micropropagated plants after 18 to 20 months of field transfer. Further, clonal fidelity of the two years old micropropagated plants was established by studying mitotic and meiotic chromosomal behavior and also considered the chromosome number and structural organization. There were no alterations in chromosome phenotypes, somatic haploid (pollen mitosis) and diploid chromosome count (n = 7; 2n = 14), or meiotic behavior. Randomly amplified polymorphic DNA analyses revealed there were no somaclonal variations among these regenerants.ConclusionsThese results confirm the very reliable method for large scale production of true-to-type plantlets of A. vera, which can be used for commercial purpose.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-46) contains supplementary material, which is available to authorized users.

Altered Cohesin Gene Dosage Affects Mammalian Meiotic Chromosome Structure and Behavior

Based on studies in mice and humans, cohesin loss from chromosomes during the period of protracted meiotic arrest appears to play a major role in chromosome segregation errors during female meiosis. In mice, mutations in meiosis-specific cohesin genes cause meiotic disturbances and infertility. However, the more clinically relevant situation, heterozygosity for mutations in these genes, has not been evaluated. We report here evidence from the mouse that partial loss of gene function for either Smc1b or Rec8 causes perturbations in the formation of the synaptonemal complex (SC) and affects both synapsis and recombination between homologs during meiotic prophase. Importantly, these defects increase the frequency of chromosomally abnormal eggs in the adult female. These findings have important implications for humans: they suggest that women who carry mutations or variants that affect cohesin function have an elevated risk of aneuploid pregnancies and may even be at increased risk of transmitting structural chromosome abnormalities.

The meiotic nuclear lamina regulates chromosome dynamics and promotes efficient homologous recombination in the mouse.

The nuclear lamina is the structural scaffold of the nuclear envelope and is well known for its central role in nuclear organization and maintaining nuclear stability and shape. In the past, a number of severe human disorders have been identified to be associated with mutations in lamins. Extensive research on this topic has provided novel important clues about nuclear lamina function. These studies have contributed to the knowledge that the lamina constitutes a complex multifunctional platform combining both structural and regulatory functions. Here, we report that, in addition to the previously demonstrated significance for somatic cell differentiation and maintenance, the nuclear lamina is also an essential determinant for germ cell development. Both male and female mice lacking the short meiosis-specific A-type lamin C2 have a severely defective meiosis, which at least in the male results in infertility. Detailed analysis revealed that lamin C2 is required for telomere-driven dynamic repositioning of meiotic chromosomes. Loss of lamin C2 affects precise synapsis of the homologs and interferes with meiotic double-strand break repair. Taken together, our data explain how the nuclear lamina contributes to meiotic chromosome behaviour and accurate genome haploidization on a mechanistic level.

Cytogenetic studies on meiotic chromosome behaviors in sterile Oriental x Trumpet lily

In order to determine the reasons for pollen sterility in lily hybrids, four diploid sterile Oriental x Trumpet (OT) lily cultivars ('Nymph', 'Gluhwein', 'Yelloween', and 'Shocking') were used to investigate the meiotic chromosome behaviors in pollen mother cells (PMCs), using genomic in situ hybridization and conventional cytological methods. At metaphase I, chromosome associations were quite variable, not only among different genotypes but also in different PMCs of the same genotype. In addition to bivalents, a certain amount of univalent, trivalents, and quadrivalents were observed in all of the investigated genotypes. In addition, ring octavalents and ring hexavalents were observed in 'Nymph'. Even dodecavalents were observed in 'Nymph'. These abnormal chromosome associations at metaphase I implied the occurrence of chromosome interchanges (translocation) in these intersectional hybrids. At anaphase-telophase, a large number of laggard chromosomes and different kinds of chromosome bridge configurations were observed. At the tetrad stage, micronuclei and polyads were also found in many PMCs. All of these abnormal chromosome behaviors in PMCs were responsible for the pollen sterility in lily hybrids.

Mitotic and meiotic behavior of rye chromosomes in wheat - Psathyrostachys huashanica amphiploid x triticale progeny

The dynamics of rye chromosomes during mitosis and meiosis was analyzed in a subset comprising 33 F3 lines from the cross of wheat, Psathyrostachys huashanica amphiploid (AABBDDNsNs) and hexaploid triticale (AABBRR), as visualized by genomic in situ hybridization. The results indicated that 31 of the total lines contained 4-14 rye chromosomes. Twenty-eight combinations had more rye chromosomes than the F1 hybrids, suggesting the occurrence of spontaneous quantitative increment. No P. huashanica chromosomes were detected in all of the combinations tested. Mitotic analysis showed that rye chromosomes progressed normally with the wheat counterparts without loss. However, abnormal meiosis was found in almost all lines. Similar progression between wheat and rye genomes appeared from interphase to metaphase I. It was at anaphase I that many rye univalents lagged behind those of wheat, followed by equational division. This resulted in the formation of chromosomal segments and micronuclei at telophase I or II. Micronuclei could also be generated from the immobilized univalents in the periphery of cells. Synapsis and translocations between wheat and rye genomes, chromosome bridges, and unreduced gametes were detected. Therefore, it is proposed that rye chromosome elimination may involve chromatid lagging, fragmentation and micronucleation, or the immobilization of certain univalents during meiosis instead of mitosis in the relatively advanced generations. This mechanism, together with spontaneous incremental increase of rye chromosome number, permitted the generation of various germplasms for wheat improvement.

Meiotic behavior of small chromosomes in maize

The typical behavior of chromosomes in meiosis is that homologous pairs synapse, recombine, and then separate at anaphase I. At anaphase II, sister chromatids separate. However, studies of small chromosomes in maize derived from a variety of sources typically have failure of sister chromatid cohesion at anaphase I. This failure occurs whether there is pairing of two copies of a minichromosome or not. These characteristics have implications for managing the transmission of the first generation artificial chromosomes in plants. Procedures to address these issues of minichromosomes are discussed.

Molecular cytogenetic analysis of wheat – Elymus repens introgression lines with resistance to Fusarium head blight

Elymus repens (L.) Gould (2n = 6x = 42, StStStStHH) is a hexaploid perennial wheatgrass species from the tribe Triticeae, distantly related to bread wheat Triticum aestivum L. (2n = 6x = 42, AABBDD). As a potential source of resistance to Fusarium head blight (FHB), E. repens was crossed to common wheat to transfer resistance genes. The progeny were advanced to homozygosity by single seed descent. A total of eight BC(1)F(9) progeny lines were selected and characterized in this study. The chromosome numbers of these derived lines ranged from 42 to 56, including lines with 44, 52, and 54 chromosomes. All of the lines were cytologically stable in terms of meiotic chromosome behavior. The univalent frequency in the lines varied between 0.34 and 2.36 per cell. Similarly, the multivalent frequency did not exceed 1% in any of the lines. GISH analysis revealed that the number of intact wheat chromosomes in the various lines varied between 40 and 44. Numerous translocated chromosomes were detected in all lines. The translocations involved chromosomal segments from wheat, and the St and H genomes of E. repens. Furthermore, trigenomic translocated chromosomes were detected in some of the lines. The introgression into wheat chromosomes included not only terminal types but also interstitial segments. The Fusarium head blight resistance of the eight lines, following point inoculation, varied from 5.65% infected florets to 11.46% compared with the check cultivars T. aestivum 'Roblin' and T. aestivum 'Crocus' at 100% and 85%, respectively.

Germinação das sementes e análise citogenética em duas espécies de palmeiras

<p><em>Euterpe edulis </em>e <em>Archontophoenix alexandrae </em>são palmeiras usadas para ornamentação e extração do palmito. Foram avaliados a germinação e o IVG das sementes, o comportamento dos cromossomos mitóticos e meióticos e a quantificação de pólen viável. Para cada espécie, em cada localidade e em cada substrato, foram usadas 60 sementes. As análises dos cromossomos mitóticos e a identificação diferencial dos nucléolos foram feitas na zona meristemática da raiz primária. Os corantes usados foram giemsa 2% (m/v) e AgNO3 50% (m/v), respectivamente. A análise dos cromossomos na microsporogênese e a viabilidade do pólen foram feitas em anteras de botões florais, coradas com carmin propiônico 2% (m/v). A maior porcentagem de germinação e IVG das sementes, nas duas espécies, foi observada nas amostras provenientes de Maquiné em substrato contendo vermiculita. <em>A. alexandrae </em>é um diploide com 2n=2x=32 cromossomos com fórmula cariotípica 14m+12sm+4st+2t. <em>E. edulis </em>é um diploide com 2n=2x=36 cromossomos com fórmula cariotípica 16m+12sm+8t. Ambas possuem um par de cromossomos submetacêntricos com constrição secundária intermediária, contendo nucléolos com genes ribossomais ativos. Nas duas espécies, análises da microsporogênese e pólen mostraram alto percentual de células normais em todas as fases da meiose I e II, resultando elevados índice meiótico (tétrades normais) e viabilidade do pólen, indicando que estas são espécies nas quais os genes se expressam normalmente nas condições ambientais em que vivem e não apresentam problemas na formação de células reprodutoras masculinas.</p>

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.

A simple method of chromosome doubling using colchicine in Torenia (Linderniaceae), and the behavior of meiotic chromosomes in amphidiploids

A simple method of chromosome doubling using colchicine in Torenia (Linderniaceae), and the behavior of meiotic chromosomes in amphidiploids

A New Species and Taxonomic Studies inTrigonellasect.Ellipticae(Fabaceae) in Iran

Trigonella yasujensis Ranjbar, Hajmoradi & Karamian sp. nova (Fabaceae) of T. sect. Ellipticae is described and illustrated from a single locality between Lordegan and Yasuj in the Zagros Mountains, Iran. It is closely related to T. elliptica but differs from it in a few morphological and anatomical characters. The meiotic chromosome number and behaviour were studied for T. yasujensis. It is a diploid species and possesses 2n = 2x = 16 chromosome number, consistent with the proposed base number x = 8. The general meiotic behaviour of the species was regular with normal bivalent pairing and chromosome segregation at meiosis. However, some meiotic abnormalities were observed including various degrees of sticky chromosomes with laggards, asynchronous nuclei, bridges and cytomixis.

Chromosome Studies of Astyanax jacuhiensis Cope, 1894 (Characidae) from the Tramandai River Basin, Brazil, Using in situ Hybridization with the 18S rDNA Probe, DAPI and CMA3 Staining

The genus Astyanax comprises 86 species of fish distributed in Brazilian river basins and is considered of the Incertae sedis group within the family Characidae. This study presents an analysis of 12 specimens of Astyanax jacuhiensis from the Tramandai River Basin, RS Brazil: 6 from the Maquiné River and 6 from the Quadros Lagoon. All specimens showed a diploid number equal to 50 chromosomes with different karyotypic formula between the two localities. The population from the Maquiné River showed 10m+26sm+6st+8a (FN=92). Fish from the Quadros Lagoon showed 12m+20sm+6st+12a (FN=88). AgNORs were evidenced in the short arm of one acrocentric chromosome pair in both populations, confirmed by FISH with the 18S rDNA probe. CMA3 fluorochrome corresponded with the AgNOR sites, while DAPI staining was negative in these regions. C banding revealed that heterochromatin was weakly distributed, mainly in the pericentromeric and terminal regions in most chromosomes. Analyses of male gonadal tissue were conducted with the objective of characterizing the meiotic chromosome behavior in A. jacuhiensis. The following stages were evidenced: spermatogonial with 50 chromosomes, pachytene and metaphase I with 25 bivalents, and metaphase II with 25 chromosomes, thus confirming the diploid number of the species. Chromosomal abnormalities were not observed. This study shows preliminary data on A. jacuhiensis from the Tramandai River Basin, contributing with more chromosomal information for this group of fish.

High Resolution Analysis of Meiotic Chromosome Structure and Behaviour in Barley (Hordeum vulgare L.)

Reciprocal crossing over and independent assortment of chromosomes during meiosis generate most of the genetic variation in sexually reproducing organisms. In barley, crossovers are confined primarily to distal regions of the chromosomes, which means that a substantial proportion of the genes of this crop rarely, if ever, engage in recombination events. There is potentially much to be gained by redistributing crossovers to more proximal regions, but our ability to achieve this is dependent upon a far better understanding of meiosis in this species. This study explores the meiotic process by describing with unprecedented resolution the early behaviour of chromosomal domains, the progression of synapsis and the structure of the synaptonemal complex (SC). Using a combination of molecular cytogenetics and advanced fluorescence imaging, we show for the first time in this species that non-homologous centromeres are coupled prior to synapsis. We demonstrate that at early meiotic prophase the loading of the SC-associated structural protein ASY1, the cluster of telomeres, and distal synaptic initiation sites occupy the same polarised region of the nucleus. Through the use of advanced 3D image analysis, we show that synapsis is driven predominantly from the telomeres, and that new synaptic initiation sites arise during zygotene. In addition, we identified two different SC configurations through the use of super-resolution 3D structured illumination microscopy (3D-SIM).