Studies on gametogenesis in Gyrinicola batrachiensis (Walton, 1929) (Oxyuroidea: Nematoda)

1981 ◽  
Vol 59 (7) ◽  
pp. 1368-1376 ◽  
Author(s):  
M. L. Adamson
Keyword(s):  
Chromosome Pairing ◽  
Meiotic Division ◽  
Diploid Number ◽  
Polar Body ◽  
Rana Clamitans ◽  
First Report ◽  
Bivalent Formation ◽  
Normal Meiosis

Cytological aspects of gametogenesis were investigated in populations of Gyrinicola batrachiensis (Oxyuroidea; Nematoda) from various anuran hosts. Populations parasitizing Rana clamitans reproduced by haplodiploidy. Females had eight chromosomes and oocytes underwent normal meiosis. Fertilized eggs containing eight chromosomes and unfertilized eggs containing four chromosomes were observed in the uterus of females. Males had four chromosomes and spermatozoa were produced mitotically. This is the first report of haplodiploidy in a nematode. Populations of G. batrachiensis parasitizing tadpoles in ponds where R. clamitans was absent reproduced by apomictic thelytoky. Females had six, seven, or eight chromosomes depending on the strain. There was no chromosome pairing nor bivalent formation. A diploid number of univalents divided to form a single polar body and a pronucleus. Apomictic strains of G. batrachiensis probably arose when mutations supressed the first meiotic division in haplodiploid strains. Apomictic females do not need to locate a mate and can begin to reproduce as soon as they are mature. Gyrinicola batrachiensis occurs only in the tadpole stage and apomictic strains are most successful in anurans in which the tadpole stage is brief.

Studies on gametogenesis in Tachygonetria vivipara Wedl, 1862 and Thelandros alatus Wedl, 1862 (Oxyuroidea; Nematoda) from Uromastix acanthinurus in Morocco

1983 ◽  
Vol 61 (10) ◽  
pp. 2357-2360 ◽  
Author(s):  
Martin L. Adamson ◽  
Annie J. Petter
Keyword(s):  
Life Cycle ◽  
Chromosome Pairing ◽  
Diploid Number ◽  
In Utero ◽  
Female Progeny ◽  
New Host ◽  
Transformation Zone ◽  
Bivalent Formation

Chromosome changes during gametogenesis in Thelandros alatus and Tachygonetria vivipara, pharyngodonids (Oxyuroidea; Nematoda) from Uromastix acanthinurus from Morocco, indicate that both species are haplodiploid. Meiosis was normal in females of Thelandros alatus. There were five bivalents, indicating a diploid number of 10 chromosomes. Most embryos in utero contained 5 chromosomes but one was observed with 10. Spermatogonial divisions contained five chromosomes; there was no evidence of chromosome pairing nor bivalent formation in males and divisions in the transformation zone of the testis contained five chromosomes with fuzzy outlines. There was no evidence of chromosome pairing nor bivalent formation in males of Tachygonetria vivipara. Oviparous and ovoviviparous females were examined. Three bivalents formed indicating a diploid number of six chromosomes. Chromosomes were counted in 179 embryos from 79 oviparous females; 128 were diploid (i.e., female) and 51 were haploid (i.e., male). It is suggested that the life cycle of T. vivipara resembles that of Gyrinicola batrachiensis: hosts are colonized by thick-shelled eggs, most of which develop into ovoviviparous females, and these females, if not fecundated, produce males parthenogenetically which develop in the same host. After being fecundated (sometimes by way of mother-son matings) the same females produce oviparous female progeny which develop in the same host. Eggs from oviparous females colonize a new host.

scholarly journals Mixed segregation of chromosomes during single-division meiosis of Saccharomyces cerevisiae.

Genetics ◽  
1990 ◽  
Vol 125 (3) ◽  
pp. 475-485
Author(s):  
G Sharon ◽  
G Simchen
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Meiotic Division ◽  
Chromosome Pair ◽  
Yeast Cells ◽  
Cell Divisions ◽  
Dyad Analysis ◽  
Normal Meiosis ◽  
Segregation Of Chromosomes

Abstract Normal meiosis consists of two consecutive cell divisions in which all the chromosomes behave in a concerted manner. Yeast cells homozygous for the mutation cdc5, however, may be directed through a single meiotic division of a novel type. Dyad analysis of a cdc5/cdc5 strain with centromere-linked markers on four different chromosomes has shown that, in these meioses, some chromosomes within a given cell segregate reductionally whereas others segregate equationally. The choice between the two types of segregation in these meioses is made individually by each chromosome pair. Different chromosome pairs exhibit different segregation tendencies. Similar results were obtained for cells homozygous for cdc14.

CHROMOSOME PAIRING IN POA ANNUA L.

1973 ◽  
Vol 15 (3) ◽  
pp. 549-551 ◽  
Author(s):  
W. M. Ellis ◽  
B. T. O. Lee ◽  
D. M. Calder
Keyword(s):  
Chromosome Pairing ◽  
Breeding System ◽  
Tetraploid Plant ◽  
Poa Annua ◽  
Diploid Population ◽  
Bivalent Formation

Cytological studies carried out on six tetraploid and one diploid population and a synthesized tetraploid plant have shown regular bivalent formation at meiosis. This regularity appears to be genetically controlled in this species. Plants from all the populations behave as diploids. The implications of this regular disomic chromosome pairing on recombination, variation and the breeding system of P. annua are considered.

Participation of the ubiquitin-proteasome pathway in rat oocyte activation

Zygote ◽  
2005 ◽  
Vol 13 (1) ◽  
pp. 87-95 ◽  
Author(s):  
Xin Tan ◽  
An Peng ◽  
Yong-Chao Wang ◽  
Yue Wang ◽  
Qing-Yuan Sun
Keyword(s):  
Meiotic Division ◽  
Polar Body ◽  
Meiotic Spindle ◽  
Oocyte Activation ◽  
Parthenogenetic Activation ◽  
Ubiquitin Proteasome Pathway ◽  
Ubiquitin Proteasome ◽  
Proteasome Pathway ◽  
Second Polar Body

The role of the ubiquitin-proteasome pathway (UPP) in mitosis is well known. However, its role in meiotic division is still poorly documented, especially in the activation of mammalian oocytes. In this study, the role of proteasome in the spontaneous and parthenogenetic activation of rat oocytes was investigated. We found that ALLN, an inhibitor of proteasome, when applied to metaphase II oocytes, inhibited spontaneous activation, blocked extrusion of the second polar body (PB) and caused the withdrawal of the partially extruded second PB. ALLN also inhibited the parthenogenetic activation induced by cycloheximide, but had no effect on the formation of pronuclei in activated eggs. In metaphase and anaphase, ubiquitin and proteasome localized to the meiotic spindle, concentrating on both sides of the oocyte–second PB boundary during PB extrusion. This pattern of cellular distribution suggests that UPP may have a role in regulating nuclear division and cytokinesis. Ubiquitin was seen to form a ring around the pronucleus, whereas proteasome was evenly distributed in the pronuclear region. Taken together, our results indicate that (1) UPP is required for the transitions of oocytes from metaphase II to anaphase II and from anaphase II to the end of meiosis; and (2) the UPP plays a role in cytokinesis of the second meiotic division.

032. Cdh1: A CELL CYCLE PROTEIN INVOLVED IN FEMALE MEIOSIS AND PREVENTION OF ANEUPLOIDY

2010 ◽  
Vol 22 (9) ◽  
pp. 10
Author(s):  
K. T. Jones
Keyword(s):  
Meiotic Division ◽  
Polar Body ◽  
Single Copy ◽  
Cyclin B1 ◽  
Cell Cycle Protein ◽  
Prophase I ◽  
First Polar Body ◽  
A Cell

Mammalian oocytes are arrested at the dictyate stage of prophase I in the ovary. In growing follicles, oocytes can become responsive to Luteinising Hormone and will undergo meiotic resumption just before ovulation. During the first meiotic division, homologous chromosomes are segregated, a process that is very error prone in human oocytes. By ovulation the oocyte has extruded its first polar body and has re-arrested at metaphase of the first meiotic division. Recent work from our lab has established that the protein Cdh1 is involved uniquely in both in the process of prophase I arrest and the correct segregation of homologs in meiosis I. Thus in cultured oocytes, in vitro antisense knockdown of Cdh1 induces both meiotic resumption and high rates of aneuploidy as a result of non-disjunction during first meiosis. Cdh1 causes prophase I arrest by inducing cyclin B1 degradation and maintaining low levels of the kinase CDK1, whose activity induces meiotic resumption. Cdh1 is an activator of the Anaphase-Promoting Complex (APC), a ubiquitin ligase that earmarks proteins such as cyclin B1 for proteolysis. Cdh1 prevents aneuploidy by causing the degradation of Cdc20, a protein that is responsible for activating the APC once all homologs are correctly aligned at metaphase. Thus loss of Cdh1 seems to prematurely activate APC(Cdc20) activity. It is interesting that a single protein can affect two important meiotic transitions in oocytes. However to explore its functions more fully, and confirm that an in vitro knockdown is faithfully replicated by in vivo loss, a targeted knockout of Cdh1 is needed. Therefore we have generated an oocyte specific Cdh1 knockout by ZP3 promoter driven Cre- recombinase activity in oocytes carrying loxP insertions in the single copy Cdh1 gene. This talk will therefore focus on the effects of an in vivo Cdh1 knockout.

scholarly journals Assembly and Positioning of the Oocyte Meiotic Spindle

2018 ◽  
Vol 34 (1) ◽  
pp. 381-403 ◽  
Author(s):  
Binyam Mogessie ◽  
Kathleen Scheffler ◽  
Melina Schuh
Keyword(s):  
Menstrual Cycle ◽  
Recent Work ◽  
Meiotic Division ◽  
Polar Body ◽  
Mitotic Division ◽  
Model System ◽  
Small Cell ◽  
Meiotic Spindle ◽  
Polar Body Extrusion ◽  
Shed Light

Fertilizable eggs develop from diploid precursor cells termed oocytes. Once every menstrual cycle, an oocyte matures into a fertilizable egg in the ovary. To this end, the oocyte eliminates half of its chromosomes into a small cell termed a polar body. The egg is then released into the Fallopian tube, where it can be fertilized. Upon fertilization, the egg completes the second meiotic division, and the mitotic division of the embryo starts. This review highlights recent work that has shed light on the cytoskeletal structures that drive the meiotic divisions of the oocyte in mammals. In particular, we focus on how mammalian oocytes assemble a microtubule spindle in the absence of centrosomes, how they position the spindle in preparation for polar body extrusion, and how the spindle segregates the chromosomes. We primarily focus on mouse oocytes as a model system but also highlight recent insights from human oocytes.

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 SIGNIFICANCE OF MEIOTIC CHROMOSOME PAIRING IN TETRAPLOID (2n = 28) BROMUS PUMPELLIANUS SCRIBN. SSP. DICKSONII

1972 ◽  
Vol 14 (4) ◽  
pp. 763-771 ◽  
Author(s):  
K. C. Armstrong
Keyword(s):  
Chromosome Pairing ◽  
High Frequency ◽  
Chiasma Frequency ◽  
Karyotype Analysis ◽  
Meiotic Chromosome ◽  
Low Frequency ◽  
Meiotic Chromosome Pairing ◽  
Ring Bivalents ◽  
Bivalent Formation

Bivalent formation was predominant at meiosis in B. pumpellianus ssp. dicksonii. The average in 15 plants ranged from 11.38 to 13.77 bivalents per cell. The high chiasma frequency (23.41-26.74) was a reflection of the high frequency of ring bivalents (9.48-12.42). A low frequency of quadrivalents occurred (0.06-1.22). A karyotype of this species was presented from both a highly contracted and moderately contracted cell and the differences between these two were noted. Four satellites were found, two large and two minute. There were 3-5 submedian and 5-7 median chromosomes depending on the cell studied. In addition two subterminal chromosomes were present. The meiotic and karyotype analysis suggest a deviation from an autotetraploid behaviour, but the presence of quadrivalents and similarities between pairs in the karyotype suggested closely related genomes. Alternatively it was considered that the quadrivalents could be due to translocation heterozygotes. The implications of these results were discussed in relation to the reported meiotic events in the octoploids, B. inermis and B. pumpellianus.

GENOME RELATIONSHIPS IN BROMUS ERECTUS, B. PUMPELLIANUS SSP. DICKSONII AND B. PUMPELLIANUS

1975 ◽  
Vol 17 (3) ◽  
pp. 391-394
Author(s):  
K. C. Armstrong
Keyword(s):  
Genetic Control ◽  
Chromosome Pairing ◽  
Low Frequency ◽  
Homoeologous Chromosome ◽  
Homoeologous Chromosome Pairing ◽  
Bivalent Formation ◽  
Bromus Erectus

Chromosome pairing was studied in hexaploid (2n = 42) hybrids of B. erectus (2n = 28) × B. pumpellianus (2n = 56) and B. pumpellianus ssp. dicksonii (2n = 28) × B. pumpellianus. Chromosome pairing in the B. erectus × B. pumpellianus hybrid was complete with predominantly bivalent formation and a low frequency of quadrivalents. The pairing results support the contention that B. pumpellianus is an autoalloploid with an AAAABBBB genome formula. The B. pumpellianus ssp. dicksonii × B. pumpellianus hybrid has an AAABBB genome formula. The presence of quadrivalents, hexavalents and cells containing a total number of bivalents or bivalents plus trivalents in excess of 14 indicated pairing between the A and B genomes. However, a high univalent frequency showed that the A and B genomes were homoeologous rather than homologous. Evidence for genetic control of homoeologous chromosome pairing and homoeologous differentiation between the genomes of the species is discussed.

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