CHROMOSOME ASSOCIATIONS IN THE FIRST MEIOTIC DIVISION IN THREE TETRAPLOID CLONES OF VACCINIUM CORYMBOSUM L

1970 ◽  
Vol 12 (2) ◽  
pp. 316-324 ◽  
Author(s):  
G. Jelenkovic ◽  
L. F. Hough
Keyword(s):  
Relaxation Process ◽  
Chromosome Pairing ◽  
Meiotic Division ◽  
Great Majority ◽  
Vaccinium Corymbosum ◽  
Early Prophase ◽  
Chromosome Associations

The analysis of chromosome pairing in three tetraploid cultivars of Vaccinium corymbosum L. revealed chat the great majority of bivalents were involved in pseudo-multivalent associations. The number of independent bivalents (not involved in formation of multivalents) increased from diakinesis to metaphase I.The pseudo-multivalents at diakinesis and at MI are the consequence of incomplete relaxation of the synizetic knot, a dense chromatic mass observed in early prophase. Factors that might affect the relaxation process are discussed.

NON-RANDOM CHROMOSOME ASSOCIATIONS AT DIPLOTENE AND DIAKINESIS IN A TETRAPLOID CLONE OF VACCINIUM AUSTRALE SMALL

1971 ◽  
Vol 13 (2) ◽  
pp. 270-276 ◽  
Author(s):  
G. Jelenkovic ◽  
E. Harrington
Keyword(s):  
Meiotic Division ◽  
Great Majority ◽  
Late Prophase ◽  
Multivalent Formation ◽  
Chromosome Associations ◽  
Tetraploid Genotype

In a cultivated tetraploid genotype (2n=4x=48) of Vaccinium australe Small the chromosome associations at late prophase of the first meiotic division and the separation of the chromosomes at anaphase I and anaphase II were investigated.Of the 223 PMC's analyzed one quarter of them displayed only bivalent associations; the remaining displayed both bivalent and quadrivalent associations. In about 3% of the PMC's, hexavalents were observed. No univalents, trivalents or pentavalents were found. The non-randomness of the chromosome associations is interpreted as resulting from obligatory pairing and localized distal chiasma.In spite of multivalent formation, in 115 PMC's studied, separation of the chromosomes at anaphase I is regular and in 95 daughter nuclei 24 chromosomes were counted. At anaphase II, the great majority of the nuclei revealed regular separation of the chromosomes and consequently numerically balanced gametes are produced.

Unorthodox male meiosis in Trichosia pubescens (Sciaridae). Chromosome elimination involves polar organelle degeneration and monocentric spindles in first and second division

1994 ◽  
Vol 107 (1) ◽  
pp. 299-312 ◽  
Author(s):  
H. Fuge
Keyword(s):  
Meiotic Division ◽  
Metaphase Plate ◽  
Chromosome Elimination ◽  
Spindle Pole ◽  
Male Meiosis ◽  
Early Prophase ◽  
Late Prophase ◽  
Section Electron ◽  
The One ◽  
Polar Organelle

Male meiosis in Trichosia pubescens (Sciaridae) was investigated by means of serial section electron microscopy and immunofluorescence light microscopy. From earlier studies of another sciarid fly, Sciara coprophila (Phillips (1967) J. Cell. Biol. 33, 73–92), it is known that the spindle poles in sciarid spermatogonia are characterized by pairs of ‘giant centrioles’, ring-shaped organelles composed of large numbers of singlet microtubules. In the present study spermatocytes in early prophase of Trichosia were found to possess single giant centrioles at opposite sides of the nucleus. The obvious reduction in centriole number from the spermatogonial to the spermatocyte stage is suggested to be the result of a suppression of daughter centriole formation. In late prophase, a large aster is developed around the centriole at one pole. At the opposite pole no comparable aster is formed. Instead, a number of irregular centriolar components appear in this region, a process that is understood to be a degeneration of the polar organelle. The components of the degenerate pole migrate into a cytoplasmic protrusion (‘bud’), which later is also utilized for the elimination of paternal chromosomes. The existence of only one functional polar centre is the reason for the formation of a monopolar monocentric spindle in first meiotic division, which in turn is one of the prerequisites for the elimination of paternal chromosomes. While the set of maternal and L chromosomes orientates and probably moves towards the pole, paternal chromosomes seem to be unable to contact the pole, possibly due to an inactivation of their kinetochores. Retrograde (‘away from the pole’) chromosome motion not involving kinetochores is assumed. Eventually, paternal chromosomes move into the pole-distal bud and are eliminated by casting off, together with the components of the degenerate polar organelle. Chromosome elimination can be delayed until the second meiotic division. The spindle of the second meiotic division is bipolar and monocentric. One spindle pole is marked by the polar centre of first division. The opposite spindle apex is devoid of a polar centre. It is assumed that spindle bipolarity in the second division is induced by the amphi-orientated chromosomes themselves. The maternal and L chromosome set (except the non-disjunctional X chromosome, which is found near the polar centre) congress in a metaphase plate, divide and segregate. Of the two daughter nuclei resulting from the second meiotic division, the one containing the X chromatids is retained as the nucleus of the future spermatozoon. The other nucleus becomes again eliminated within a second cytoplasmic bud.

scholarly journals Analysis of chromosome pairing and breakage in pearl millet

1982 ◽  
Vol 40 (2) ◽  
pp. 165-174 ◽  
Author(s):  
Prasad R. K. Koduru ◽  
T. G. K. Murthy ◽  
K. V. Lakshmi ◽  
M. Krishna Rao
Keyword(s):  
Quantitative Analysis ◽  
Pearl Millet ◽  
Chromosome Pairing ◽  
Mutant Gene ◽  
Pollen Grain ◽  
Early Prophase ◽  
Chromosome Fragmentation ◽  
Reduced Frequency ◽  
Synchronous Development ◽  
The Relationship

SUMMARYThe relationship between chromosome pairing and chromosome fragmentation has been studied in a gene controlled mutant of pearl millet (2n = 14). Premeiotic mitosis, premeiotic cell development and early prophase I are normal without any fragments, which first appear at pachytene. The extent of fragmentation varies from zero to very extreme with two discrete classes of plants, namely those with partial fragmentation and those with multiple fragmentation. A quantitative analysis of bivalent distribution and the distribution of AI bridges in desynaptic and fragmented cells show all of them to be nonrandom events. We suggest that in cells showing partial fragmentation the bridges and fragments result from U-type exchanges at pachytene. The reduced frequency of AII bridges indicates relatively low sister chromatid reunion at pachytene. In multiple fragmented plants numerous minute fragments were seen from pachytene. Despite these anomalies most PMCs complete meiosis but subsequently abort at the pollen grain stage. The mutant gene also causes disturbances in the sequence of meiotic development in the ear and in the synchronous development of PMCs within an anther. It has no effect on the tapetum or on the physiological development of the anther.

scholarly journals Comparison of Pollen Characteristics, Meiotic Division and Chromosome Pairing between Diploid and Tetraploid Shinano Walnut (Juglans regia L. cv. Mitsuru)

2003 ◽  
Vol 72 (2) ◽  
pp. 134-140
Author(s):  
Masao Yajima ◽  
Yasumitu Watanabe ◽  
Katuto Yanagisawa ◽  
Shigeru Shomura ◽  
Seiji Chino ◽  
...  
Keyword(s):  
Chromosome Pairing ◽  
Meiotic Division ◽  
Juglans Regia

THE CYTOGENETIC STRUCTURE OF A 56-CHROMOSOME DERIVATIVE FROM A CROSS BETWEEN TRITICUM AESTIVUM AND AGROPYRON ELONGATUM (2n = 70)

1976 ◽  
Vol 18 (2) ◽  
pp. 271-279 ◽  
Author(s):  
Jan Dvořák
Keyword(s):  
Triticum Aestivum ◽  
Chromosome Pairing ◽  
Chinese Spring ◽  
Wheat Chromosome ◽  
Agropyron Elongatum ◽  
Synthetic Genome ◽  
Chromosome Associations ◽  
Chromosome Segments ◽  
The Relationship ◽  
Chromosome 3B

Chromosome pairing was studied in a number of hybrids involving a 56-chromosome wheat-Agropyron derivative, PW 327. PW 327 originated from the cross, Triticum aestivum cv. Chinese Spring (Chinese Spring × A. elongatum, 2n = 70). In hybrids between PW 327 and T. aestivum a number of multivalent chromosome associations were formed at metaphase I. These multivalents result from interchanges which occurred among wheat chromosomes 1A, 1D, 2A, 2D, 4D and 6D of PW 327. One chromosome of the Agropyron chromosome set of PW 327 occasionally pairs with wheat chromosome 3B. The rest of the Agropyron chromosomes present in PW 327 do not pair with the chromosomes of T. aestivum. It is proposed that the set of Agropyron chromosomes present in PW 327 is not an intact genome of decaploid A. elongatum but rather a modified synthetic genome combining chromosomes and/or chromosome segments from different genomes of the Agropyron parent. The incorporation of duplication-deletions into synthetic genomes of natural polyploids is discussed and it is shown that the set of Agropyron chromosomes which is present in PW 327 carries at least one such duplication-deletion. Pairing between chromosomes of diploid and decaploid A. elongatum was studied in a 56-chromosome hybrid from a cross between an amphiploid, T. aestivum × A. elongatum (2n = 14), and PW 327. It appeared that at least four chromosomes of these two Agropyrons occasionally paired with each other in this hybrid in which the diploidizing system of wheat was active. The relationship between chromosomes of diploid and decaploid A. elongatum is discussed.

Assessment of chromosome associations in haploids and their parental accessions in Hordeum

Genome ◽  
1988 ◽  
Vol 30 (2) ◽  
pp. 204-210 ◽  
Author(s):  
R. von Bothmer ◽  
N. C. Subrahmanyam
Keyword(s):  
Genetic Variation ◽  
Chromosome Pairing ◽  
Diploid Species ◽  
Meiotic Behaviour ◽  
Meiotic Pairing ◽  
Homoeologous Pairing ◽  
Homoeologous Chromosome ◽  
Homologous Pairing ◽  
Homoeologous Chromosome Pairing ◽  
Chromosome Associations

Meiotic pairing was studied in the following species and their haploid derivatives: Hordeum cordobense 2x, H. marinum 2x and 4x, H. secalinum 4x, H. capense 4x, H. jubatum 4x, H. brachyantherum 4x and 6x, H. lechleri 6x, and H. procerum 6x. The study revealed (i) homologous pairing in diploid species and very little nonhomologous associations in their mono-haploids; (ii) the alloploid nature of the polyploid taxa; (iii) a certain degree of homoeologous pairing in polyhaploids despite the diploid-like meiotic behaviour of the polyploids; (iv) genetic variation in the suppression of homoeologous chromosome pairing in different Hordeum species.Key words: Hordeum, meiotic pairing, haploids.

scholarly journals Sex Chromosome Pairing Mediated by Euchromatic Homology in Drosophila Male Meiosis

Genetics ◽  
2020 ◽  
Vol 214 (3) ◽  
pp. 605-616 ◽  
Author(s):  
Christopher A. Hylton ◽  
Katie Hansen ◽  
Andrew Bourgeois ◽  
John E. Tomkiel Dean
Keyword(s):  
Sex Chromosome ◽  
Intergenic Spacer ◽  
Male Meiosis ◽  
Early Prophase ◽  
Dna Breaks ◽  
Late Prophase ◽  
Prophase I ◽  
Double Strand Dna Breaks ◽  
Chromosome Associations ◽  
Meiosis I

Diploid germline cells must undergo two consecutive meiotic divisions before differentiating as haploid sex cells. During meiosis I, homologs pair and remain conjoined until segregation at anaphase. Drosophila melanogaster spermatocytes are unique in that the canonical events of meiosis I including synaptonemal complex formation, double-strand DNA breaks, and chiasmata are absent. Sex chromosomes pair at intergenic spacer sequences within the ribosomal DNA (rDNA). Autosomes pair at numerous euchromatic homologies, but not at heterochromatin, suggesting that pairing may be limited to specific sequences. However, previous work generated from genetic segregation assays or observations of late prophase I/prometaphase I chromosome associations fail to differentiate pairing from maintenance of pairing (conjunction). Here, we separately examined the capability of X euchromatin to pair and conjoin using an rDNA-deficient X and a series of Dp(1;Y) chromosomes. Genetic assays showed that duplicated X euchromatin can substitute for endogenous rDNA pairing sites. Segregation was not proportional to homology length, and pairing could be mapped to nonoverlapping sequences within a single Dp(1;Y). Using fluorescence in situ hybridization to early prophase I spermatocytes, we showed that pairing occurred with high fidelity at all homologies tested. Pairing was unaffected by the presence of X rDNA, nor could it be explained by rDNA magnification. By comparing genetic and cytological data, we determined that centromere proximal pairings were best at segregation. Segregation was dependent on the conjunction protein Stromalin in Meiosis, while the autosomal-specific Teflon was dispensable. Overall, our results suggest that pairing may occur at all homologies, but there may be sequence or positional requirements for conjunction.

CHROMOSOME ASSOCIATIONS AT DIAKINESIS IN THE CULTIVATED STRAWBERRY

1971 ◽  
Vol 13 (2) ◽  
pp. 231-236 ◽  
Author(s):  
D. W. S. Mok ◽  
W. D. Evans
Keyword(s):  
Chromosome Pairing ◽  
Genetic Data ◽  
Cytological Evidence ◽  
Tetrasomic Inheritance ◽  
Secondary Pairing ◽  
Multivalent Formation ◽  
Chromosome Associations

The analysis of chromosome pairing in the cultivated strawberry revealed that multivalent formation occurs in each of the nine cultivars examined. Secondary pairing and a loose association of bivalents were also observed. The cytological evidence suggests that tetrasomic inheritance should be considered in the interpretation of genetic data.

scholarly journals The telomere bouquet is a hub where meiotic double-strand breaks, synapsis, and stable homolog juxtaposition are coordinated in the zebrafish, Danio rerio

2018 ◽  
Author(s):  
Yana P. Blokhina ◽  
An D. Nguyen ◽  
Bruce W. Draper ◽  
Sean M. Burgess
Keyword(s):  
Chromosome Pairing ◽  
Danio Rerio ◽  
Genetic Information ◽  
Homologous Chromosome ◽  
Double Strand Breaks ◽  
Early Prophase ◽  
Strand Breaks ◽  
Homologous Chromosomes ◽  
Homologous Chromosome Pairing ◽  
Males And Females

AbstractMeiosis is a cellular program that generates haploid gametes for sexual reproduction. While chromosome events that contribute to reducing ploidy (homologous chromosome pairing, synapsis, and recombination) are well conserved, their execution varies across species and even between sexes of the same species. The telomere bouquet is a conserved feature of meiosis that was first described nearly a century ago, yet its role is still debated. Here we took advantage of the prominent telomere bouquet in zebrafish, Danio rerio, and super-resolution microscopy to show that axis morphogenesis, synapsis, and the formation of double-strand breaks (DSBs) all take place within the immediate vicinity of telomeres. We established a coherent timeline of events and tested the dependence of each event on the formation of Spo11-induced DSBs. First, we found that the axis protein Sycp3 loads adjacent to telomeres and extends inward, suggesting a specific feature common to all telomeres seeds the development of the axis. Second, we found that newly formed axes near telomeres engage in presynaptic co-alignment by a mechanism that depends on DSBs, even when stable juxtaposition of homologous chromosomes at interstitial regions is not yet evident. Third, we were surprised to discover that ~30% of telomeres in early prophase I engage in associations between two or more chromosome ends and these interactions decrease in later stages. Finally, while pairing and synapsis were disrupted in both spo11 males and females, their reproductive phenotypes were starkly different; spo11 mutant males failed to produce sperm while females produced offspring with severe developmental defects. Our results support zebrafish as an important vertebrate model for meiosis with implications for differences in fertility and genetically derived birth defects in males and females.Author SummaryInherent to reproduction is the transmission of genetic information from one generation to the next. In sexually reproducing organisms, each parent contributes an equal amount of genetic information, packaged in chromosomes, to the offspring. Diploid organisms, like humans, have two copies of every chromosome, while their haploid gametes (e.g. eggs and sperm) have only one. This reduction in ploidy depends on the segregation of chromosomes during meiosis, resulting in gametes with one copy of each chromosome. Missegregation of the chromosomes in the parents leads to abnormal chromosome numbers in the offspring, which is usually lethal or has detrimental developmental effects. While it has been known for over a century that homologous chromosomes pair and recombine to facilitate proper segregation, how homologs find their partners has remained elusive. A structure that has been central to the discussion of homolog pairing is the bouquet, or the dynamic clustering of telomeres during early stages of meiosis. Here we use zebrafish to show that the telomere bouquet is the site where key events leading to homologous chromosome pairing are coordinated. Furthermore, we show that deletion of spo11, a gene required for proper recombination in most studied organisms, resulted in very different effects in males and females where males were sterile while females produced deformed progeny.

Quantitative analysis of meiotic chromosome pairing in triploid blueberry: evidence for preferential pairing

Genome ◽  
1990 ◽  
Vol 33 (1) ◽  
pp. 60-67 ◽  
Author(s):  
Nicholi Vorsa
Keyword(s):  
Chromosome Pairing ◽  
Meiotic Chromosome ◽  
Chiasma Formation ◽  
Vaccinium Corymbosum ◽  
Preferential Pairing ◽  
Frequency Distributions ◽  
Meiotic Chromosome Pairing ◽  
Random Pairing ◽  
Random Frequency ◽  
Genome Divergence

Mathematical models have been developed to predict meiotic configuration frequency distributions for autoploid (random chromosome pairing) or preferential chromosome pairing behavior. Meiotic chromosome pairing was quantitatively analysed, relative to these models, in six highbush blueberry (Vaccinium corymbosum) triploid (2n = 3x = 36) hybrids derived from three unrelated 4x × 2x crosses. Mean trivalent per cell frequencies ranged from 3.59 to 7.89. Excess univalents were observed in triploids of one cross and are probably a result of disturbance in chiasma formation or maintenance and (or) random pairing failure. Arm chiasmate association values (a and b) ranged from 0.72 to 1.00, with the greatest difference in arm values being 0.18. Trivalent to ring bivalent (r) ratios ranged from 0.59 to 2.02. The observed configuration frequency distributions of three triploids having r-values greater than 1 did not deviate significantly from the autoploid pairing (p = 0) model frequency distribution. Frequency distributions of three triploids having r-values less than 1 deviated significantly from the autoploid model. Ranges for pairing affinity relationships include the possibility of two genomes pairing preferentially at a frequency of 77.7% (0.444 points over the random frequency of 0.333), which suggests the presence of genome divergence in blueberry. However, violation of model assumptions could seriously bias preferential pairing estimates. Segregating genetic factors also appear to be of significance in chromosome pairing behavior.Key words: autotriploids, chromosome pairing, preferential pairing, genome divergence, meiotic configurations.

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