Meiosis: A type of CELL NUCLEUS division, occurring during maturation of the GERM CELLS. Two successive cell nucleus divisions following a single chromosome duplication (S PHASE) result in daughter cells with half the number of CHROMOSOMES as the parent cells.Chromosome Pairing: The alignment of CHROMOSOMES at homologous sequences.Spermatocytes: Male germ cells derived from SPERMATOGONIA. The euploid primary spermatocytes undergo MEIOSIS and give rise to the haploid secondary spermatocytes which in turn give rise to SPERMATIDS.Spores, Fungal: Reproductive bodies produced by fungi.Chromosome Segregation: The orderly segregation of CHROMOSOMES during MEIOSIS or MITOSIS.Synaptonemal Complex: The three-part structure of ribbon-like proteinaceous material that serves to align and join the paired homologous CHROMOSOMES. It is formed during the ZYGOTENE STAGE of the first meiotic division. It is a prerequisite for CROSSING OVER.Oocytes: Female germ cells derived from OOGONIA and termed OOCYTES when they enter MEIOSIS. The primary oocytes begin meiosis but are arrested at the diplotene state until OVULATION at PUBERTY to give rise to haploid secondary oocytes or ova (OVUM).Meiotic Prophase I: The prophase of the first division of MEIOSIS (in which homologous CHROMOSOME SEGREGATION occurs). It is divided into five stages: leptonema, zygonema, PACHYNEMA, diplonema, and diakinesis.Prophase: The first phase of cell nucleus division, in which the CHROMOSOMES become visible, the CELL NUCLEUS starts to lose its identity, the SPINDLE APPARATUS appears, and the CENTRIOLES migrate toward opposite poles.Crossing Over, Genetic: The reciprocal exchange of segments at corresponding positions along pairs of homologous CHROMOSOMES by symmetrical breakage and crosswise rejoining forming cross-over sites (HOLLIDAY JUNCTIONS) that are resolved during CHROMOSOME SEGREGATION. Crossing-over typically occurs during MEIOSIS but it may also occur in the absence of meiosis, for example, with bacterial chromosomes, organelle chromosomes, or somatic cell nuclear chromosomes.Nondisjunction, Genetic: The failure of homologous CHROMOSOMES or CHROMATIDS to segregate during MITOSIS or MEIOSIS with the result that one daughter cell has both of a pair of parental chromosomes or chromatids and the other has none.Spermatogenesis: The process of germ cell development in the male from the primordial germ cells, through SPERMATOGONIA; SPERMATOCYTES; SPERMATIDS; to the mature haploid SPERMATOZOA.Chromatids: Either of the two longitudinally adjacent threads formed when a eukaryotic chromosome replicates prior to mitosis. The chromatids are held together at the centromere. Sister chromatids are derived from the same chromosome. (Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)Recombination, Genetic: Production of new arrangements of DNA by various mechanisms such as assortment and segregation, CROSSING OVER; GENE CONVERSION; GENETIC TRANSFORMATION; GENETIC CONJUGATION; GENETIC TRANSDUCTION; or mixed infection of viruses.Pachytene Stage: The stage in the first meiotic prophase, following ZYGOTENE STAGE, when CROSSING OVER between homologous CHROMOSOMES begins.Centromere: The clear constricted portion of the chromosome at which the chromatids are joined and by which the chromosome is attached to the spindle during cell division.Chromosomes: In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)Mitosis: A type of CELL NUCLEUS division by means of which the two daughter nuclei normally receive identical complements of the number of CHROMOSOMES of the somatic cells of the species.Metaphase: The phase of cell nucleus division following PROMETAPHASE, in which the CHROMOSOMES line up across the equatorial plane of the SPINDLE APPARATUS prior to separation.Cell Cycle Proteins: Proteins that control the CELL DIVISION CYCLE. This family of proteins includes a wide variety of classes, including CYCLIN-DEPENDENT KINASES, mitogen-activated kinases, CYCLINS, and PHOSPHOPROTEIN PHOSPHATASES as well as their putative substrates such as chromatin-associated proteins, CYTOSKELETAL PROTEINS, and TRANSCRIPTION FACTORS.Oogenesis: The process of germ cell development in the female from the primordial germ cells through OOGONIA to the mature haploid ova (OVUM).Chromosomes, Fungal: Structures within the nucleus of fungal cells consisting of or containing DNA, which carry genetic information essential to the cell.Schizosaccharomyces pombe Proteins: Proteins obtained from the species Schizosaccharomyces pombe. The function of specific proteins from this organism are the subject of intense scientific interest and have been used to derive basic understanding of the functioning similar proteins in higher eukaryotes.Schizosaccharomyces: A genus of ascomycetous fungi of the family Schizosaccharomycetaceae, order Schizosaccharomycetales.Saccharomyces cerevisiae: A species of the genus SACCHAROMYCES, family Saccharomycetaceae, order Saccharomycetales, known as "baker's" or "brewer's" yeast. The dried form is used as a dietary supplement.Haploidy: The chromosomal constitution of cells, in which each type of CHROMOSOME is represented once. Symbol: N.Spindle Apparatus: A microtubule structure that forms during CELL DIVISION. It consists of two SPINDLE POLES, and sets of MICROTUBULES that may include the astral microtubules, the polar microtubules, and the kinetochore microtubules.Germ Cells: The reproductive cells in multicellular organisms at various stages during GAMETOGENESIS.Saccharomyces cerevisiae Proteins: Proteins obtained from the species SACCHAROMYCES CEREVISIAE. The function of specific proteins from this organism are the subject of intense scientific interest and have been used to derive basic understanding of the functioning similar proteins in higher eukaryotes.Testis: The male gonad containing two functional parts: the SEMINIFEROUS TUBULES for the production and transport of male germ cells (SPERMATOGENESIS) and the interstitial compartment containing LEYDIG CELLS that produce ANDROGENS.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Diploidy: The chromosomal constitution of cells, in which each type of CHROMOSOME is represented twice. Symbol: 2N or 2X.Anaphase: The phase of cell nucleus division following METAPHASE, in which the CHROMATIDS separate and migrate to opposite poles of the spindle.Chromosomal Proteins, Non-Histone: Nucleoproteins, which in contrast to HISTONES, are acid insoluble. They are involved in chromosomal functions; e.g. they bind selectively to DNA, stimulate transcription resulting in tissue-specific RNA synthesis and undergo specific changes in response to various hormones or phytomitogens.Proto-Oncogene Proteins c-mos: Cellular proteins encoded by the c-mos genes (GENES, MOS). They function in the cell cycle to maintain MATURATION PROMOTING FACTOR in the active state and have protein-serine/threonine kinase activity. Oncogenic transformation can take place when c-mos proteins are expressed at the wrong time.Kinetochores: Large multiprotein complexes that bind the centromeres of the chromosomes to the microtubules of the mitotic spindle during metaphase in the cell cycle.Gametogenesis: The process of germ cell development from the primordial GERM CELLS to the mature haploid GAMETES: ova in the female (OOGENESIS) or sperm in the male (SPERMATOGENESIS).Fungal Proteins: Proteins found in any species of fungus.Gametogenesis, Plant: The process of germ cell development in plants, from the primordial PLANT GERM CELLS to the mature haploid PLANT GAMETES.Cyclin B: A cyclin subtype that is transported into the CELL NUCLEUS at the end of the G2 PHASE. It stimulates the G2/M phase transition by activating CDC2 PROTEIN KINASE.Starfish: Echinoderms having bodies of usually five radially disposed arms coalescing at the center.Nuclear Proteins: Proteins found in the nucleus of a cell. Do not confuse with NUCLEOPROTEINS which are proteins conjugated with nucleic acids, that are not necessarily present in the nucleus.Spermatids: Male germ cells derived from the haploid secondary SPERMATOCYTES. Without further division, spermatids undergo structural changes and give rise to SPERMATOZOA.Spermatozoa: Mature male germ cells derived from SPERMATIDS. As spermatids move toward the lumen of the SEMINIFEROUS TUBULES, they undergo extensive structural changes including the loss of cytoplasm, condensation of CHROMATIN into the SPERM HEAD, formation of the ACROSOME cap, the SPERM MIDPIECE and the SPERM TAIL that provides motility.Sex Chromosomes: The homologous chromosomes that are dissimilar in the heterogametic sex. There are the X CHROMOSOME, the Y CHROMOSOME, and the W, Z chromosomes (in animals in which the female is the heterogametic sex (the silkworm moth Bombyx mori, for example)). In such cases the W chromosome is the female-determining and the male is ZZ. (From King & Stansfield, A Dictionary of Genetics, 4th ed)Caenorhabditis elegans: A species of nematode that is widely used in biological, biochemical, and genetic studies.Genes, Fungal: The functional hereditary units of FUNGI.Aneuploidy: The chromosomal constitution of cells which deviate from the normal by the addition or subtraction of CHROMOSOMES, chromosome pairs, or chromosome fragments. In a normally diploid cell (DIPLOIDY) the loss of a chromosome pair is termed nullisomy (symbol: 2N-2), the loss of a single chromosome is MONOSOMY (symbol: 2N-1), the addition of a chromosome pair is tetrasomy (symbol: 2N+2), the addition of a single chromosome is TRISOMY (symbol: 2N+1).Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Coprinus: A genus of black-spored basidiomycetous fungi of the family Coprinaceae, order Agaricales; some species are edible.DNA Breaks, Double-Stranded: Interruptions in the sugar-phosphate backbone of DNA, across both strands adjacently.Separase: Separase is a caspase-like cysteine protease, which plays a central role in triggering ANAPHASE by cleaving the SCC1/RAD21 subunit of the cohesin complex. Cohesin holds the sister CHROMATIDS together during METAPHASE and its cleavage results in chromosome segregation.Caenorhabditis elegans Proteins: Proteins from the nematode species CAENORHABDITIS ELEGANS. The proteins from this species are the subject of scientific interest in the area of multicellular organism MORPHOGENESIS.Chromosomes, Plant: Complex nucleoprotein structures which contain the genomic DNA and are part of the CELL NUCLEUS of PLANTS.Maturation-Promoting Factor: Protein kinase that drives both the mitotic and meiotic cycles in all eukaryotic organisms. In meiosis it induces immature oocytes to undergo meiotic maturation. In mitosis it has a role in the G2/M phase transition. Once activated by CYCLINS; MPF directly phosphorylates some of the proteins involved in nuclear envelope breakdown, chromosome condensation, spindle assembly, and the degradation of cyclins. The catalytic subunit of MPF is PROTEIN P34CDC2.Ovum: A mature haploid female germ cell extruded from the OVARY at OVULATION.Oogonia: Euploid female germ cells of an early stage of OOGENESIS, derived from primordial germ cells during ovarian differentiation. Oogonia undergo MEIOSIS and give rise to haploid OOCYTESFertilization: The fusion of a spermatozoon (SPERMATOZOA) with an OVUM thus resulting in the formation of a ZYGOTE.Pollen: The fertilizing element of plants that contains the male GAMETOPHYTES.Microtubules: Slender, cylindrical filaments found in the cytoskeleton of plant and animal cells. They are composed of the protein TUBULIN and are influenced by TUBULIN MODULATORS.DNA, Fungal: Deoxyribonucleic acid that makes up the genetic material of fungi.Cell Nucleus: Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (CELL NUCLEOLUS). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the ENDOPLASMIC RETICULUM. A cell may contain more than one nucleus. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)Cholestenes: Steroids with methyl groups at C-10 and C-13 and a branched 8-carbon chain at C-17. Members include compounds with any degree of unsaturation; however, CHOLESTADIENES is available for derivatives containing two double bonds.Gene Expression Regulation, Fungal: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control of gene action in fungi.Polar Bodies: Minute cells produced during development of an OOCYTE as it undergoes MEIOSIS. A polar body contains one of the nuclei derived from the first or second meiotic CELL DIVISION. Polar bodies have practically no CYTOPLASM. They are eventually discarded by the oocyte. (from King & Stansfield, A Dictionary of Genetics, 4th ed)Spermatogonia: Euploid male germ cells of an early stage of SPERMATOGENESIS, derived from prespermatogonia. With the onset of puberty, spermatogonia at the basement membrane of the seminiferous tubule proliferate by mitotic then meiotic divisions and give rise to the haploid SPERMATOCYTES.Sister Chromatid Exchange: An exchange of segments between the sister chromatids of a chromosome, either between the sister chromatids of a meiotic tetrad or between the sister chromatids of a duplicated somatic chromosome. Its frequency is increased by ultraviolet and ionizing radiation and other mutagenic agents and is particularly high in BLOOM SYNDROME.Ovary: The reproductive organ (GONADS) in female animals. In vertebrates, the ovary contains two functional parts: the OVARIAN FOLLICLE for the production of female germ cells (OOGENESIS); and the endocrine cells (GRANULOSA CELLS; THECA CELLS; and LUTEAL CELLS) for the production of ESTROGENS and PROGESTERONE.Saccharomycetales: An order of fungi in the phylum Ascomycota that multiply by budding. They include the telomorphic ascomycetous yeasts which are found in a very wide range of habitats.Rad51 Recombinase: A Rec A recombinase found in eukaryotes. Rad51 is involved in DNA REPAIR of double-strand breaks.Protein-Serine-Threonine Kinases: A group of enzymes that catalyzes the phosphorylation of serine or threonine residues in proteins, with ATP or other nucleotides as phosphate donors.Phenotype: The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.Alleles: Variant forms of the same gene, occupying the same locus on homologous CHROMOSOMES, and governing the variants in production of the same gene product.Parthenogenesis: A unisexual reproduction without the fusion of a male and a female gamete (FERTILIZATION). In parthenogenesis, an individual is formed from an unfertilized OVUM that did not complete MEIOSIS. Parthenogenesis occurs in nature and can be artificially induced.DNA-Binding Proteins: Proteins which bind to DNA. The family includes proteins which bind to both double- and single-stranded DNA and also includes specific DNA binding proteins in serum which can be used as markers for malignant diseases.Endodeoxyribonucleases: A group of enzymes catalyzing the endonucleolytic cleavage of DNA. They include members of EC 3.1.21.-, EC 3.1.22.-, EC 3.1.23.- (DNA RESTRICTION ENZYMES), EC 3.1.24.- (DNA RESTRICTION ENZYMES), and EC 3.1.25.-.Cyclin A1: A cyclin A subtype primarily found in male GERM CELLS. It may play a role in the passage of SPERMATOCYTES into meiosis I.Models, Genetic: Theoretical representations that simulate the behavior or activity of genetic processes or phenomena. They include the use of mathematical equations, computers, and other electronic equipment.X Chromosome: The female sex chromosome, being the differential sex chromosome carried by half the male gametes and all female gametes in human and other male-heterogametic species.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Y Chromosome: The male sex chromosome, being the differential sex chromosome carried by half the male gametes and none of the female gametes in humans and in some other male-heterogametic species in which the homologue of the X chromosome has been retained.Crosses, Genetic: Deliberate breeding of two different individuals that results in offspring that carry part of the genetic material of each parent. The parent organisms must be genetically compatible and may be from different varieties or closely related species.Telophase: The final phase of cell nucleus division following ANAPHASE, in which two daughter nuclei are formed, the CYTOPLASM completes division, and the CHROMOSOMES lose their distinctness and are transformed into CHROMATIN threads.Aurora Kinase C: Aurora kinase C is a chromosomal passenger protein that interacts with aurora kinase B in the regulation of MITOSIS. It is found primarily in GERM CELLS in the TESTIS, and may mediate CHROMOSOME SEGREGATION during SPERMATOGENESIS.Anaphase-Promoting Complex-Cyclosome: An E3 ubiquitin ligase primarily involved in regulation of the metaphase-to-anaphase transition during MITOSIS through ubiquitination of specific CELL CYCLE PROTEINS. Enzyme activity is tightly regulated through subunits and cofactors, which modulate activation, inhibition, and substrate specificity. The anaphase-promoting complex, or APC-C, is also involved in tissue differentiation in the PLACENTA, CRYSTALLINE LENS, and SKELETAL MUSCLE, and in regulation of postmitotic NEURONAL PLASTICITY and excitability.Chromosome Mapping: Any method used for determining the location of and relative distances between genes on a chromosome.Apomixis: Asexual reproduction resulting in the formation of viable seeds from FLOWERS without fertlization (i.e. use of POLLEN). Progeny plants produced from apomictic seeds are perfect clones of the parent.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Cyclin B1: A cyclin B subtype that colocalizes with MICROTUBULES during INTERPHASE and is transported into the CELL NUCLEUS at the end of the G2 PHASE.Gene Expression Regulation, Developmental: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control of gene action during the developmental stages of an organism.Prometaphase: The phase of cell nucleus division following PROPHASE, when the breakdown of the NUCLEAR ENVELOPE occurs and the MITOTIC SPINDLE APPARATUS enters the nuclear region and attaches to the KINETOCHORES.Aurora Kinases: A family of highly conserved serine-threonine kinases that are involved in the regulation of MITOSIS. They are involved in many aspects of cell division, including centrosome duplication, SPINDLE APPARATUS formation, chromosome alignment, attachment to the spindle, checkpoint activation, and CYTOKINESIS.Plant Infertility: The failure of PLANTS to complete fertilization and obtain seed (SEEDS) as a result of defective POLLEN or ovules, or other aberrations. (Dict. of Plant Genet. and Mol. Biol., 1998)DNA Repair: The reconstruction of a continuous two-stranded DNA molecule without mismatch from a molecule which contained damaged regions. The major repair mechanisms are excision repair, in which defective regions in one strand are excised and resynthesized using the complementary base pairing information in the intact strand; photoreactivation repair, in which the lethal and mutagenic effects of ultraviolet light are eliminated; and post-replication repair, in which the primary lesions are not repaired, but the gaps in one daughter duplex are filled in by incorporation of portions of the other (undamaged) daughter duplex. Excision repair and post-replication repair are sometimes referred to as "dark repair" because they do not require light.Drosophila Proteins: Proteins that originate from insect species belonging to the genus DROSOPHILA. The proteins from the most intensely studied species of Drosophila, DROSOPHILA MELANOGASTER, are the subject of much interest in the area of MORPHOGENESIS and development.Oncogene Proteins v-mos: Transforming proteins coded by mos oncogenes. The v-mos proteins were originally isolated from the Moloney murine sarcoma virus (Mo-MSV).In Situ Hybridization, Fluorescence: A type of IN SITU HYBRIDIZATION in which target sequences are stained with fluorescent dye so their location and size can be determined using fluorescence microscopy. This staining is sufficiently distinct that the hybridization signal can be seen both in metaphase spreads and in interphase nuclei.CDC2 Protein Kinase: Phosphoprotein with protein kinase activity that functions in the G2/M phase transition of the CELL CYCLE. It is the catalytic subunit of the MATURATION-PROMOTING FACTOR and complexes with both CYCLIN A and CYCLIN B in mammalian cells. The maximal activity of cyclin-dependent kinase 1 is achieved when it is fully dephosphorylated.Histones: Small chromosomal proteins (approx 12-20 kD) possessing an open, unfolded structure and attached to the DNA in cell nuclei by ionic linkages. Classification into the various types (designated histone I, histone II, etc.) is based on the relative amounts of arginine and lysine in each.Homologous Recombination: An exchange of DNA between matching or similar sequences.Cdc20 Proteins: Highly conserved proteins that specifically bind to and activate the anaphase-promoting complex-cyclosome, promoting ubiquitination and proteolysis of cell-cycle-regulatory proteins. Cdc20 is essential for anaphase-promoting complex activity, initiation of anaphase, and cyclin proteolysis during mitosis.

*  The Nucleoporin Nup2 Contains a Meiotic-Autonomous Region that Promotes the Dynamic Chromosome Events of Meiosis | Genetics
1997 Meiosis-specific DNA double-strand breaks are catalyzed by Spo11, a member of a widely conserved protein family. Cell 88: ... The nup2Δ ndj1Δ double mutant gives a more severe meiosis defect compared to the single mutants, including a delay in the ... 2011 The Aurora kinase Ipl1 is necessary for spindle pole body cohesion during budding yeast meiosis. J. Cell Sci. 124: 2891- ... MEIOSIS is a cellular program that creates haploid gametes from diploid parent cells. Ploidy is reduced through two chromosome ...
  http://www.genetics.org/content/206/3/1319
*  Zygotene Stage of Meiosis in Plants
... Zygotene is the stage of meiotic prophase which instantly follows the leptotene and during ... Zygotene Stage of Meiosis in Plants. Zygotene is the stage of meiotic prophase which instantly follows the leptotene and during ...
  http://www.qsstudy.com/biology/zygotene-stage-meiosis-plants
*  DIGITAL.CSIC: Meiotic checkpoint control of chromosome dynamics
Defects in these processes, such as those resulting from the absence of the S. cerevisiae Zip1 protein, activate a meiosis- ... Resumen del trabajo presentado al Fundación Ramon Areces International Symposium The biology of meiosis: implications for ... International Symposium: The biology of meiosis: implications for fertility and genetic disorders (2015). ...
  http://digital.csic.es/handle/10261/157890
*  4.2 Meiosis - BIOLOGY4IBDP
Outline how the process of meiosis can lead to Down's Syndrome 4marks. Accept any of the points below if clearly drawn and ... This can also occur in second division of meiosis; sister chromatids fail to separate; Fertilisation with one gamete / sperm / ... Reduction division occurs during meiosis; Homologous chromosomes pair up (in middle of cell); Each chromosome in homologous ... Cell undergoes first division/meiosis I/cytokinesis; chromosomes separate again; two cells from first division undergo second ...
  http://biology4ibdp.weebly.com/42-meiosis.html
*  Advances in Plant Meiosis: From Model Species to Crops | Frontiers Research Topic
Plants were in the forefront of the study of meiosis in the first half of the 20th century. The pioneering work of Creighton ... achievements of plant meiosis have been mainly based on the isolation of mutants and genes involved in the meiotic control. ... This Research Topic addresses the fundamental mechanisms of meiosis in both model and crop plants, as well as their implication ... chromosome dynamics in meiosis. - control of crossover distribution. - meiosis in polyploids. - interspecific recombination. We ...
  https://www.frontiersin.org/research-topics/6093/advances-in-plant-meiosis-from-model-species-to-crops
*  Meiosis - Meiosis I - Chromosome, Genetic, Chromatids, and Sister - JRank Articles
Meiosis - The Sources Of Genetic Diversity [next] [back] Meiosis - Overview Citing this material. Please include a link to this ... Thus, each chromosome enters meiosis consisting of two sister chromatids joined at the centromere. The first stage of meiosis ... Other Free Encyclopedias » Medicine Encyclopedia » Genetics in Medicine - Part 3 » Meiosis - Overview, Meiosis I, The Sources ... Meiosis must be preceded by the S phase of the cell cycle. This is when DNA replication (the copying of the genetic material) ...
  http://medicine.jrank.org/pages/2497/Meiosis-Meiosis-I.html
*  Meiosis - definition of meiosis by The Free Dictionary
meiosis synonyms, meiosis pronunciation, meiosis translation, English dictionary definition of meiosis. meiosis top to bottom: ... In meiosis a parent cell replicates and recombines, divides once to create two daughter cells, then divides again creating four ... meiosis. Also found in: Thesaurus, Medical, Encyclopedia, Wikipedia. meiosis. top to bottom:In meiosis a parent cell replicates ... meiosis. [maɪˈəʊsɪs] n → meiosi f. mei·o·sis n. meiosis, proceso de subdivisión celular que resulta en la formación de gametos ...
  https://www.thefreedictionary.com/meiosis
*  Spindle assembly checkpoint and its regulators in meiosis. - Semantic Scholar
A similar mechanism has been uncovered for meiosis in the last decade, especially in the past several years. METHODS For this ... Evidence for the existence of SAC functions in meiosis is provided by studies on the SAC proteins mitotic-arrest deficient-1 ( ... Errors in chromosome segregation during meiosis will result in aneuploidy, followed by loss of the conceptus during pregnancy ... CONCLUSIONS SAC and its regulators exist and function in meiosis, and their malfunctions may cause germ cell aneuploidy. ...
  https://www.semanticscholar.org/paper/Spindle-assembly-checkpoint-and-its-regulators-in-Sun-Kim/113d62918db300b64439d1266a193734611f7614
*  The Arabidopsis homologue of Xrcc3 plays an essential role in meiosis | The EMBO Journal
Meiosis is severely disrupted in atxrcc3 plants. To further characterize the atxrcc3 sterility phenotype, we followed meiosis ... AtXrcc3 is essential for postsynaptic events in meiosis. Diplotene and later stages of atxrcc3 meiosis show the presence of ... Garcia V, Bruchet H, Camescasse D, Granier F, Bouchez D, Tissier A (2003) AtATM is essential for meiosis and the somatic ... Bishop DK, Park D, Xu L, Kleckner N (1992) DMC1: a meiosis‐specific yeast homolog of E. coli recA required for recombination, ...
  http://emboj.embopress.org/content/23/2/439?ijkey=b942735c4de3c36e6e4fc541bc1dadf43e896e61&keytype2=tf_ipsecsha
*  Category:Meiosis - Wikimedia Commons
Meiosis (261 36)- Dividing pollen mother cells M I, A I, T I (metaphase I, anaphase I, telophase I) - Lilium plant.jpg 3,751 × ... Media in category "Meiosis". The following 145 files are in this category, out of 145 total. ... Retrieved from "https://commons.wikimedia.org/w/index.php?title=Category:Meiosis&oldid=257531702" ...
  https://commons.wikimedia.org/wiki/Meiosis
*  Mitosis and Meiosis
The cell cycle as well as individual steps of mitosis and meiosis are included in this learning material. ... are used to help participants understand the differences between and steps involved in mitosis and meiosis. ... MERLOT description and link to 'Meiosis in an Animal Cell,' which provides a user-friendly, interactive animation for meiosis. ... MERLOT description and link to 'Meiosis Animation,' which includes animations, descriptions, and questions about meiosis.. ...
  https://serc.carleton.edu/sp/merlot/biology/visualizations/examples/48527.html
*  Corn Meiosis slides
... Kathleen Pelkki pelkki at svsu.edu Mon Oct 8 14:55:51 EST 2001 *Previous message: Molecular Geneticist ... Does anyone know of this gentleman and if he stills sells these slides? They are the best for studying meiosis... very clear ... Hi, all! About 10 years ago we purchased prepared microscope slides of corn meiosis from a Mr. Hsu in Kentucky. ...
  http://www.bio.net/bionet/mm/plant-ed/2001-October/007194.html
*  Aug 20, 2009
meiosis backpack designed by davidi gilad, is an equipment bag which was developed to utilize the physical properties of the ... meiosis is made up of polygonal shapes creating a shell all images courtesy of davidi gilad ... the colors of meiosis blend in with the skyline of greys and blues ... why is it called meiosis? has it anything to do with sex cell division? ...
  https://www.designboom.com/design/meiosis-backpack-by-davidi-gilad/
*  Meiosis | edHelper.com
Meiosis. Life Science Meiosis Print Meiosis Reading Comprehension with Sixth Grade Work. Print Meiosis Reading Comprehension. ... Feedback on Meiosis Leave your feedback on Meiosis (use this link if you found an error in the story). ... These cells, called gametes, form by a type of cell division called meiosis. Cells formed through meiosis have only half the ... duplication, haploid, meiosis, replicate, sexual, fertilization, anaphase, diploid, interphase, metaphase, prophase, telophase ...
  https://www.edhelper.com/ReadingComprehension_54_49.html
*  What is meiosis terminology? | Reference.com
Some important meiosis terms include chromosomes, nucleus, cell and genetic... ... Meiosis terminology is a vocabulary of words that are necessary to understand and explain the process of meiosis. ... Where does meiosis occur?. A: Meiosis occurs in the reproductive organs of all males and females. The process of meiosis ... When does meiosis occur in humans?. A: Meiosis in humans happens before birth in females, and constantly after puberty in males ...
  https://www.reference.com/science/meiosis-terminology-61abc67fc4ec655a
*  Meiosis - Medical Dictionary / Glossary | Medindia
Meiosis' - Constriction of the pupil of the eye, is clearly explained in Medindia s glossary of medical terms ... Meiosis - Glossary. Written & Compiled by Medindia Content Team. Medically Reviewed by The Medindia Medical Review Team on May ...
  https://www.medindia.net/glossary/meiosis.htm
*  Meiosis Maven | The Scientist Magazine®
Meiosis Maven. Fueled by her love of visual data and addicted to chromosomes, Abby Dernburg continues to study how homologous ... "This work is really exciting because many people think that some unusual features of C. elegans meiosis are just a 'weird worm ... I may wind up doing something not related to meiosis in the future, but I still think chromosomes are really intriguing. There ... Beyond C. elegans. Dernburg's laboratory recently branched out beyond the nematode C. elegans to study meiosis in planarians, ...
  https://www.the-scientist.com/?articles.view/articleNo/38960/title/Meiosis-Maven/
*  Meiosis - The Student Room
Exactly, there is no chromosomal replication in meiosis 2 as it occurs in meiosis 1. ... Is there no s phase in interphase of meiosis 2 because no chromosome no is duplicated?. Posted from TSR Mobile ...
  https://www.thestudentroom.co.uk/showthread.php?t=2299290
*  Meiosis Tutorial
The Biology Project , Cell Biology , Meiosis , Problems Meiosis Tutorial Problem 8: Ocean coral Coral in the ocean grows by ... The Biology Project , Cell Biology , Meiosis , Problems. The Biology Project Department of Biochemistry and Molecular ...
  http://biology.arizona.edu/cell_bio/tutorials/meiosis/08a.html
*  Recent Articles | Meiosis | The Scientist Magazine®
The Nutshell Putative Gay Genes Identified, Questioned A genomic interrogation of homosexuality turns up speculative links between genetic elements and sexual orientation, but researchers say the study is too small to be significant. ...
  https://www.the-scientist.com/?articles.list/tagNo/6193/tags/Meiosis/
*  Meiosis confusions?? - The Student Room
So basically meiosis is to produce gametes but why does your original cell have two sets of same chromosome that are homologous ...
  https://www.thestudentroom.co.uk/showthread.php?t=4508560
*  Mitosis vs Meiosis | Smore Newsletters
The differences between Mitosis and Meiosis by Ariana Camacho , This newsletter was created with Smore, an online tool for ... In Meiosis, it only occurs in Meiosis I, and does not occur prior to Meiosis II. ... In Meiosis, it only occurs in Meiosis I, and does not occur prior to Meiosis II. ... Mitosis is more common than meiosis and has a wider variety of functions. Meiosis has a narrow but significant purpose: ...
  https://www.smore.com/w8dh1
*  Mitosis and Meiosis by Steven Student on Prezi
... place/biocoach/meiosis/anai.html Anaphase I in Meiosis Telophase of Mitosis Telophase I of Meiosis In both mitosis and meiosis ... Transcript of Mitosis and Meiosis. Mitosis and Meiosis Similarities and Differences How are Mitosis and Meiosis similar? http ... meiosis/proii.html There are two cells dividing in Meiosis II because these are the two daughter cells from Meiosis I.. The ... place/biocoach/meiosis/metai.html Metaphase I in Meiosis Metaphase in Mitosis Anaphase of Mitosis Anaphase I of Meiosis The ...
  https://prezi.com/mwe5cqg5_zi7/mitosis-and-meiosis/
*  Meiosis - Simple English Wikipedia, the free encyclopedia
Meiosis can be divided into meiosis I and meiosis II.. Meiosis I[change , change source]. The function of the first division is ... For that reason, meiosis is often called reduction division. In the long run, meiosis increases genetic variation, in a way ... Meiosis is a special type of cell division. Unlike mitosis, the way normal body cells divide, meiosis results in cells that ... All eukaryotes that reproduce sexually use meiosis. This also includes many single-celled organisms. Meiosis does not occur in ...
  https://simple.wikipedia.org/wiki/Meiosis

Spermatocyte: Spermatocytes are a type of male gametocyte in animals. They derive from immature germ cells called spermatogonia.Ascospore: An ascospore is a spore contained in an ascus or that was produced inside an ascus. This kind of spore is specific to fungi classified as ascomycetes (Ascomycota).Immortal DNA strand hypothesis: The immortal DNA strand hypothesis was proposed in 1975 by John Cairns as a mechanism for adult stem cells to minimize mutations in their genomes.Cairns, J.Synaptonemal complex: right|300px|thumb|A Homologous chromosomes (light blue) align and synapse together via transverse filaments (black lines) and longitudinal filaments (dark blue). Recombination nodules (gray ellipsoids) on the central region may help in completing recombination.Oocyte selection: Oocyte selection is a procedure that is performed prior to in vitro fertilization, in order to use oocytes with maximal chances of resulting in pregnancy. In contrast, embryo selection takes place after fertilization.Prophase: Prophase (from the Greek πρό, "before" and φάσις, "stage"), is a stage of mitosis in which the chromatin condenses into double rod-shaped structures called chromosomes in which the chromatin becomes visible. This process, called chromatin condensation, is involved with the condensin complex.Establishment of sister chromatid cohesion: Sister chromatid cohesion refers to the process by which sister chromatids are paired and held together during certain phases of the cell cycle. Establishment of sister chromatid cohesion is the process by which chromatin-associated cohesin protein becomes competent to physically bind together the sister chromatids.Recombination (cosmology): In cosmology, recombination refers to the epoch at which charged electrons and protons first became bound to form electrically neutral hydrogen atoms.Note that the term recombination is a misnomer, considering that it represents the first time that electrically neutral hydrogen formed.CentromerePremature chromosome condensation: Premature chromosome condensation (PCC) occurs in eukaryotic organisms when mitotic cells fuse with interphase cells. Chromatin, a substance that contains genetic material such as DNA, is normally found in a loose bundle inside a cell's nucleus.Bookmarking: Bookmarking (also "gene bookmarking" or "mitotic bookmarking") refers to a potential mechanism of transmission of gene expression programs through cell division.Metaphase: Metaphase (from the Greek μετά, "adjacent" and φάσις, "stage") is a stage of mitosis in the eukaryotic cell cycle in which chromosomes are at their second-most condensed and coiled stage (they are at their most condensed in anaphase. These chromosomes, carrying genetic information, align in the equator of the cell before being separated into each of the two daughter cells.Schizosaccharomyces pombe: Schizosaccharomyces pombe, also called "fission yeast", is a species of yeast used in traditional brewing and as a model organism in molecular and cell biology. It is a unicellular eukaryote, whose cells are rod-shaped.Zuotin: Z-DNA binding protein 1, also known as Zuotin, is a Saccharomyces cerevisiae yeast gene.Spindle apparatus: In cell biology, the spindle apparatus refers to the subcellular structure of eukaryotic cells that separates chromosomes between daughter cells during cell division. It is also referred to as the mitotic spindle during mitosis, a process that produces genetically identical daughter cells, or the meiotic spindle during meiosis, a process that produces gametes with half the number of chromosomes of the parent cell.Blood–testis barrier: The blood–testis barrier is a physical barrier between the blood vessels and the seminiferous tubules of the animal testes. The name "blood-testis barrier" is misleading in that it is not a blood-organ barrier in a strict sense, but is formed between Sertoli cells of the seminiferous tubule and as such isolates the further developed stages of germ cells from the blood.Silent mutation: Silent mutations are mutations in DNA that do not significantly alter the phenotype of the organism in which they occur. Silent mutations can occur in non-coding regions (outside of genes or within introns), or they may occur within exons.AnaphaseChromo shadow domain: In molecular biology, the chromo shadow domain is a protein domain which is distantly related to the chromodomain. It is always found in association with a chromodomain.Kinetochore: The kinetochore is the protein structure on chromatids where the spindle fibers attach during cell division to pull sister chromatids apart.Clb 5,6 (Cdk1): Clb5 and Clb6 are B-type, S-phase cyclins in yeast that assist in cell cycle regulation.Morgan, DO (2007) 'The Cell Cycle: Principles of Control, Oxford University Press Clb5 and Clb6 bind and activate Cdk1, and high levels of these cyclins are required for entering S-phase.Pisaster ochraceusSpermatid: The spermatid is the haploid male gametid that results from division of secondary spermatocytes. As a result of meiosis, each spermatid contains only half of the genetic material present in the original primary spermatocyte.Spermiogenesis: Spermiogenesis is the final stage of spermatogenesis, which sees the maturation of spermatids into mature, motile spermatozoa. The spermatid is more or less circular cell containing a nucleus, Golgi apparatus, centriole and mitochondria.History of research on Caenorhabditis elegans: The nematode worm Caenorhabditis elegans was first studied in the laboratory by Victor Nigon and Ellsworth Dougherty in the 1940s, but came to prominence after being adopted by Sydney Brenner in 1963 as a model organism for the study of developmental biology using genetics. In 1974, Brenner published the results of his first genetic screen, which isolated hundreds of mutants with morphological phenotypes.Coles PhillipsCoprinopsis atramentaria: Coprinopsis atramentaria, commonly known as the common ink cap or inky cap, is an edible (but sometimes poisonous, see below) mushroom found in Europe and North America. Previously known as Coprinus atramentarius, it is the second best known ink cap and previous member of the genus Coprinus after C.Maturation promoting factor: Maturation-promoting factor (abbreviated MPF, also called mitosis-promoting factor or M-Phase-promoting factor) is the cyclin-Cdk complex that was discovered first in frog eggs. It stimulates the mitotic and meiotic phases of the cell cycle.Sarah R, Lotfi: Sarah R. Lotfi (b.PollenMicrotubule: Microtubules ([+ tube] + [are a component of the [[cytoskeleton], found throughout the [[cytoplasm. These tubular polymers of tubulin can grow as long as 50 micrometres and are highly dynamic.Sister (Sister2Sister song)Serine/threonine-specific protein kinasePhenotype microarray: The phenotype microarray approach is a technology for high-throughput phenotyping of cells.Infinite alleles model: The infinite alleles model is a mathematical model for calculating genetic mutations. The Japanese geneticist Motoo Kimura and American geneticist James F.Telescoping generations: Telescoping generations can occur in parthenogenetic species, such as aphids or other life forms that have the ability to reproduce without ovum fertilization. This occurrence is characterized by a viviparous female having a daughter growing inside her that is also parthenogenetically pregnant with a daughter cell.DNA-binding proteinExcinuclease: Excision endonuclease, also known as excinuclease or UV-Specific Endonuclease, is a nuclease (enzyme) which excises a fragment of nucleotides during DNA repair. The excinuclease cuts out a fragment by hydrolyzing two phosphodiester bonds, one on either side of the lesion in the DNA.Smith–Fineman–Myers syndrome: Smith–Fineman–Myers syndrome (SFMS1), also called X-linked mental retardation-hypotonic facies syndrome 1 (MRXHF1), Carpenter–Waziri syndrome, Chudley–Lowry syndrome, SFMS, Holmes–Gang syndrome and Juberg–Marsidi syndrome (JMS), is a rare X-linked recessive congenital disorder that causes birth defects. This syndrome was named after 3 men, Richard D.Protein primary structure: The primary structure of a peptide or protein is the linear sequence of its amino acid structural units, and partly comprises its overall biomolecular structure. By convention, the primary structure of a protein is reported starting from the amino-terminal (N) end to the carboxyl-terminal (C) end.PCDHY: PCDH11Y is a gene unique to human males which competes with FOXP2 for the title of the "language gene." PCDH11Y is the gene for making Protocadherin 11Y, a protein that guides the development of nerve cells.APC/C activator protein CDH1: Cdh1 is one of the substrate adaptor protein of the anaphase-promoting complex (APC) in the budding yeast Saccharomyces cerevisiae. Functioning as an activator of the APC/C, Cdh1 regulates the activity and substrate specificity of this ubiquitin E3-ligase.Chromosome regionsSymmetry element: A symmetry element is a point of reference about which symmetry operations can take place. In particular, symmetry elements can be centers of inversion, axes of rotation and mirror planes.Aurora inhibitorCytoplasmic male sterility: Cytoplasmic male sterility is total or partial male sterility in plants as the result of specific nuclear and mitochondrial interactions. Male sterility is the failure of plants to produce functional anthers, pollen, or male gametes.Base excision repair: frame|right|Basic steps of base excision repair|Basic steps of base excision repairBESS domain: In molecular biology, the BESS domain is a protein domain which has been named after the three proteins that originally defined the domain: BEAF (Boundary element associated factor 32), Suvar(3)7 and Stonewall ). The BESS domain is 40 amino acid residues long and is predicted to be composed of three alpha helices, as such it might be related to the myb/SANT HTH domain.Histone octamer: A histone octamer is the eight protein complex found at the center of a nucleosome core particle. It consists of two copies of each of the four core histone proteins (H2A, H2B, H3 and H4).

(1/6057) Meiosis: MeiRNA hits the spot.

The protein Mei2 performs at least two functions required in fission yeast for the switch from mitotic to meiotic cell cycles. One of these functions also requires meiRNA. It appears that meiRNA targets Mei2 to the nucleus, where it can promote the first meiotic division.  (+info)

(2/6057) SWM1, a developmentally regulated gene, is required for spore wall assembly in Saccharomyces cerevisiae.

Meiosis in Saccharomyces cerevisiae is followed by encapsulation of haploid nuclei within multilayered spore walls. Formation of this spore-specific wall requires the coordinated activity of enzymes involved in the biosynthesis of its components. Completion of late events in the sporulation program, leading to spore wall formation, requires the SWM1 gene. SWM1 is expressed at low levels during vegetative growth but its transcription is strongly induced under sporulating conditions, with kinetics similar to those of middle sporulation-specific genes. Homozygous swm1Delta diploids proceed normally through both meiotic divisions but fail to produce mature asci. Consistent with this finding, swm1Delta mutant asci display enhanced sensitivity to enzymatic digestion and heat shock. Deletion of SWM1 specifically affects the expression of mid-late and late sporulation-specific genes. All of the phenotypes observed are similar to those found for the deletion of SPS1 or SMK1, two putative components of a sporulation-specific MAP kinase cascade. However, epistasis analyses indicate that Swm1p does not form part of the Sps1p-Smk1p-MAP kinase pathway. We propose that Swm1p, a nuclear protein, would participate in a different signal transduction pathway that is also required for the coordination of the biochemical and morphological events occurring during the last phase of the sporulation program.  (+info)

(3/6057) Comparative sequence analysis of human minisatellites showing meiotic repeat instability.

The highly variable human minisatellites MS32 (D1S8), MS31A (D7S21), and CEB1 (D2S90) all show recombination-based repeat instability restricted to the germline. Mutation usually results in polar interallelic conversion or occasionally in crossovers, which, at MS32 at least, extend into DNA flanking the repeat array, defining a localized recombination hotspot and suggesting that cis-acting elements in flanking DNA can influence repeat instability. Therefore, comparative sequence analysis was performed to search for common flanking elements associated with these unstable loci. All three minisatellites are located in GC-rich DNA abundant in dispersed and tandem repetitive elements. There were no significant sequence similarities between different loci upstream of the unstable end of the repeat array. Only one of the three loci showed clear evidence for putative coding sequences near the minisatellite. No consistent patterns of thermal stability or DNA secondary structure were shared by DNA flanking these loci. This work extends previous data on the genomic environment of minisatellites. In addition, this work suggests that recombinational activity is not controlled by primary or secondary characteristics of the DNA sequence flanking the repeat array and is not obviously associated with gene promoters as seen in yeast.  (+info)

(4/6057) hMSH5: a human MutS homologue that forms a novel heterodimer with hMSH4 and is expressed during spermatogenesis.

MutS homologues have been identified in nearly all organisms examined to date. They play essential roles in maintaining mitotic genetic fidelity and meiotic segregation fidelity. MutS homologues appear to function as a molecular switch that signals genomic manipulation events. Here we describe the identification of the human homologue of the Saccharomyces cerevisiae MSH5, which is known to participate in meiotic segregation fidelity and crossing-over. The human MSH5 (hMSH5) was localized to chromosome 6p22-21 and appears to play a role in meiosis because expression is induced during spermatogenesis between the late primary spermatocytes and the elongated spermatid phase. hMSH5 interacts specifically with hMSH4, confirming the generality of functional heterodimeric interactions in the eukaryotic MutS homologue, which also includes hMSH2-hMSH3 and hMSH2-hMSH6.  (+info)

(5/6057) Sequential PKC- and Cdc2-mediated phosphorylation events elicit zebrafish nuclear envelope disassembly.

Molecular markers of the zebrafish inner nuclear membrane (NEP55) and nuclear lamina (L68) were identified, partially characterized and used to demonstrate that disassembly of the zebrafish nuclear envelope requires sequential phosphorylation events by first PKC, then Cdc2 kinase. NEP55 and L68 are immunologically and functionally related to human LAP2beta and lamin B, respectively. Exposure of zebrafish nuclei to meiotic cytosol elicits rapid phosphorylation of NEP55 and L68, and disassembly of both proteins. L68 phosphorylation is completely inhibited by simultaneous inhibition of Cdc2 and PKC and only partially blocked by inhibition of either kinase. NEP55 phosphorylation is completely prevented by inhibition or immunodepletion of cytosolic Cdc2. Inhibition of cAMP-dependent kinase, MEK or CaM kinase II does not affect NEP55 or L68 phosphorylation. In vitro, nuclear envelope disassembly requires phosphorylation of NEP55 and L68 by both mammalian PKC and Cdc2. Inhibition of either kinase is sufficient to abolish NE disassembly. Furthermore, novel two-step phosphorylation assays in cytosol and in vitro indicate that PKC-mediated phosphorylation of L68 prior to Cdc2-mediated phosphorylation of L68 and NEP55 is essential to elicit nuclear envelope breakdown. Phosphorylation elicited by Cdc2 prior to PKC prevents nuclear envelope disassembly even though NEP55 is phosphorylated. The results indicate that sequential phosphorylation events elicited by PKC, followed by Cdc2, are required for zebrafish nuclear disassembly. They also argue that phosphorylation of inner nuclear membrane integral proteins is not sufficient to promote nuclear envelope breakdown, and suggest a multiple-level regulation of disassembly of nuclear envelope components during meiosis and at mitosis.  (+info)

(6/6057) Characterization of a Caenorhabditis elegans recA-like gene Ce-rdh-1 involved in meiotic recombination.

A recA-like gene was identified in the Caenorhabditis elegans genome project database. The putative product of the gene, termed Ce-rdh-1 (C. elegans RAD51 and DMC1/LIM15 homolog 1), consists of 357 amino acid residues. The predicted amino acid sequence of Ce-rdh-1 showed 46-60% identity to both RAD51 type and DMC1/LIM15 type genes in several eukaryote species. The results of RNAi (RNA-mediated interference) indicated that repression of Ce-rdh-1 blocked chromosome condensation of six bivalents and dissociation of chiasmata in oocytes of F1 progeny. Oogenesis did not proceed to the diakinesis stage. Accordingly, all the eggs produced (F2) died in early stages. These results suggest that Ce-rdh-1 participates in meiotic recombination.  (+info)

(7/6057) Gene expression and chromatin organization during mouse oocyte growth.

Mouse oocytes can be classified according to their chromatin organization and the presence [surrounded nucleolus (SN) oocytes] or absence [nonsurrounded nucleolus (NSN) oocytes] of a ring of Hoechst-positive chromatin around the nucleolus. Following fertilization only SN oocytes are able to develop beyond the two-cell stage. These studies indicate a correlation between SN and NSN chromatin organization and the developmental competence of the female gamete, which may depend on gene expression. In the present study, we have used the HSP70.1Luc transgene (murine HSP70.1 promoter + reporter gene firefly luciferase) to analyze gene expression in oocytes isolated from ovaries of 2-day- to 13-week-old females. Luciferase was assayed on oocytes after classification as SN or NSN type. Our data show that SN oocytes always exhibit a higher level of luciferase activity, demonstrating a higher gene expression in this category. Only after meiotic resumption, metaphase II oocytes derived from NSN or SN oocytes acquire the same level of transgene expression. We suggest that the limited availability of transcripts and corresponding proteins, excluded from the cytoplasm until GVBD in NSN oocytes, could explain why these oocytes have a lower ability to sustain embryonic development beyond the two-cell stage at which major zygotic transcription occurs. With this study we have furthered our knowledge of epigenetic regulation of gene expression in oogenesis.  (+info)

(8/6057) Germ cell development in the XXY mouse: evidence that X chromosome reactivation is independent of sexual differentiation.

Prior to entry into meiosis, XX germ cells in the fetal ovary undergo X chromosome reactivation. The signal for reactivation is thought to emanate from the genital ridge, but it is unclear whether it is specific to the developing ovary. To determine whether the signals are present in the developing testis as well as the ovary, we examined the expression of X-linked genes in germ cells from XXY male mice. To facilitate this analysis, we generated XXY and XX fetuses carrying X chromosomes that were differentially marked and subject to nonrandom inactivation. This pattern of nonrandom inactivation was maintained in somatic cells but, in XX as well as XXY fetuses, both parental alleles were expressed in germ cell-enriched cell populations. Because testis differentiation is temporally and morphologically normal in the XXY testis and because all germ cells embark upon a male pathway of development, these results provide compelling evidence that X chromosome reactivation in fetal germ cells is independent of the somatic events of sexual differentiation. Proper X chromosome dosage is essential for the normal fertility of male mammals, and abnormalities in germ cell development are apparent in the XXY testis within several days of X reactivation. Studies of exceptional germ cells that survive in the postnatal XXY testis demonstrated that surviving germ cells are exclusively XY and result from rare nondisjunctional events that give rise to clones of XY cells.  (+info)