Does Dna Replicate Again for Meiosis Ii

Jail cell Partitioning - Meiosis

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Introduction

Meiosis is the special blazon of recombinative and reductive cell sectionalisation occurring simply in the generation of the gametes or germ cells (oocyte and spermatozoa).

For recombination, meiosis requires that homologous chromosomes are properly paired and aligned past the induction of DNA double-strand breaks by the enzyme SPO11 during the prophase of the outset meiotic division.

Meiotic cell division also reduces (halves) the chromosomal content. The overall process of germ cell development is called "gametogenesis" and includes non just meiosis but also the cellular morphological changes, that occur differently in male person and female person gametes.

Some Contempo Findings

Bivalent separation into univalents precedes historic period-related meiosis I errors in oocytes^[i]

Karyotype of parthenogenetic blastocysts^[two]

• Distinct prophase arrest mechanisms in human being male person meiosis ^[3] "To preclude chromosomal aberrations being transmitted to the offspring, strict meiotic checkpoints are in place to remove aberrant spermatocytes. Still, in about 1% of males these checkpoints cause complete meiotic arrest leading to azoospermia and subsequent infertility. Hither, nosotros unravel two clearly distinct meiotic arrest mechanisms that occur during prophase of homo male meiosis. Type I arrested spermatocytes display severe asynapsis of the homologous chromosomes, disturbed XY-trunk formation and increased expression of the Y chromosome-encoded factor c and seem to activate a Deoxyribonucleic acid damage pathway leading to induction of p63, peradventure causing spermatocyte apoptosis. Type II arrested spermatocytes display normal chromosome synapsis, normal XY-body morphology and meiotic crossover germination but have a lowered expression of several cell bike regulating genes and fail to silence the 10 chromosome-encoded gene ZFX."

• Review - Actin cytoskeleton dynamics in mammalian oocyte meiosis ^[four] "During mitosis, cells undergo symmetrical jail cell division, while oocyte meiotic maturation undergoes two consecutive, asymmetric divisions that generate a totipotent haploid oocyte and 2 small polar bodies not involved in DNA replication. This specialized division allows most maternal components be maintained in the oocytes for early embryo evolution. Nuclear positioning, germinal vesicle breakdown, spindle migration, spindle rotation, chromosome segregation, and polar body extrusion are the nigh critical cellular processes during oocyte meiosis I and Ii, and a growing number of studies primarily using the mouse oocyte model revealed that actin filaments were critical for these processes, especially for spindle migration. Several of import molecules take been reported to be involved in these processes. 1 family of molecules are the small GTPases, such as Rho GTPases, Ran GTPases, and Rab GTPases and another are the actin nucleators, such equally the formin family unit and the Arp2/3 complex. The nowadays review summarizes recent progress made regarding the roles of actin filaments in the asymmetric oocyte division." oocyte | polar body

• Inefficient Crossover Maturation Underlies Elevated Aneuploidy in Human Female Meiosis ^[five] "Meiosis is the cellular plan that underlies gamete germination. For this program, crossovers between homologous chromosomes play an essential mechanical role to ensure regular segregation. We present a detailed study of crossover germination in human male and female meiosis, enabled by modeling assay. Results suggest that recombination in the ii sexes proceeds analogously and efficiently through most stages. Even so, specifically in female person (but non male person), ∼25% of the intermediates that should mature into crossover products actually neglect to do then. Further, this "female person-specific crossover maturation inefficiency" is inferred to brand major contributions to the high level of chromosome mis-segregation and resultant aneuploidy that uniquely afflicts human female oocytes (eastward.g., giving Down syndrome). Additionally, crossover levels on different chromosomes in the same nucleus tend to co-vary, an effect attributable to global per-nucleus modulation of chromatin loop size. Maturation inefficiency could potentially reflect an evolutionary advantage of increased aneuploidy for human females."

• Contradistinct Crossover Distribution and Frequency in Spermatocytes of Infertile Men with Azoospermia ^[6] "Our study aims to narrate the crossover distribution in infertile men with non-obstructive (NOA) and obstructive azoospermia (OA) forth chromosomes 13, xviii and 21. Viii of the 16 NOA men and five of the 21 OA men in our study displayed reduced crossover frequency compared to command fertile men. Seven NOA men and nine OA men showed contradistinct crossover distributions on at least ane of the chromosome arms studied compared to controls. We establish that although both NOA and OA men displayed altered crossover distributions, NOA men may be at a higher risk of suffering both altered crossover frequencies and distributions compared to OA men."

• Review - The evolution of meiotic sex activity and its alternatives ^[7] "Meiosis is an ancestral, highly conserved process in eukaryotic life cycles, and for all eukaryotes the shared component of sexual reproduction. The benefits and functions of meiosis, all the same, are even so under discussion, especially considering the costs of meiotic sex."

More recent papers This table allows an automatic computer search of the external PubMed database using the listed "Search term" text link. This search now requires a manual link as the original PubMed extension has been disabled. The displayed list of references do not reverberate any editorial choice of material based on content or relevance. References also appear on this list based upon the appointment of the actual page viewing. References listed on the rest of the content folio and the associated discussion folio (listed under the publication year sub-headings) practice include some editorial choice based upon both relevance and availability. More? References | Discussion Page | Journal Searches | 2022 References | 2022 References Search term: Meiosis | Meiosis i | Meiosis two | Meiosis crossover | Meiotic spindle | Cohesion | chiasmata

Older papers These papers originally appeared in the Some Recent Findings table, simply as that list grew in length have at present been shuffled down to this collapsible table. Run across also the Discussion Page for other references listed past year and References on this current page. From Meiosis to Mitosis: The Astonishing Flexibility of Cell Division Mechanisms in Early on Mammalian Development [viii] "The execution of female meiosis and the establishment of the zygote is arguably the almost critical stage of mammalian development. The egg tin be arrested in the prophase of meiosis I for decades, and when information technology is activated, the spindle is assembled de novo. This spindle must part with the highest of fidelity and yet its assembly is unusually achieved in the absence of conventional centrosomes and with minimal influence of chromatin. Moreover, its dramatic asymmetric positioning is achieved through remarkable backdrop of the actin cytoskeleton to ensure elimination of the polar bodies. The second meiotic arrest marks a uniquely prolonged metaphase eventually interrupted by egg activation at fertilization to complete meiosis and marking a period of grooming of the male and female pronuclear genomes not only for their entry into the mitotic cleavage divisions but also for the imminent prospect of their zygotic expression." Silencing of X-Linked MicroRNAs by Meiotic Sex Chromosome Inactivation [9] "During the pachytene stage of meiosis in male mammals, the X and Y chromosomes are transcriptionally silenced by Meiotic Sex Chromosome Inactivation (MSCI). MSCI is conserved in therian mammals and is essential for normal male fertility. ...Here nosotros use RNA FISH to examine X-miRNA expression in the male germ line. We detect that, like poly peptide-coding X-genes, X-miRNAs are expressed prior to prophase I and are thereafter silenced during pachynema. Ten-miRNA silencing does not occur in mouse models with lacking MSCI. Furthermore, X-miRNAs are expressed at pachynema when present equally autosomally integrated transgenes. Thus, nosotros conclude that silencing of 10-miRNAs during pachynema in wild blazon males is MSCI-dependent. Chiefly, misexpression of X-miRNAs during pachynema causes spermatogenic defects. We propose that MSCI represents a chromosomal mechanism by which X-miRNAs, and other potential 10-encoded repressors, tin can be silenced, thereby regulating genes with critical late spermatogenic functions." spermatozoa Bivalent separation into univalents precedes age-related meiosis I errors in oocytes [1] "The frequency of chromosome segregation errors during meiosis I (MI) in oocytes increases with age. The 2-hit model suggests that errors are acquired past the combination of a starting time hit that creates susceptible crossover configurations and a second hit comprising an age-related reduction in chromosome cohesion. This model predicts an age-related increment in univalents, but direct evidence of this phenomenon every bit a major crusade of segregation errors has been lacking. Here, nosotros provide the first alive assay of single chromosomes undergoing segregation errors during MI in the oocytes of naturally aged mice. Chromosome tracking reveals that 80% of the errors are preceded by bivalent separation into univalents. The set of the univalents is biased towards counterbalanced and unbalanced predivision of sister chromatids during MI. Moreover, we discover univalents predisposed to predivision in human oocytes. This study defines premature bivalent separation into univalents as the principal defect responsible for age-related aneuploidy." Premature dyad separation in meiosis II is the major segregation fault with maternal age in mouse oocytes [10] "Changes consistent with chromosome cohesion deterioration were constitute with age, including increased interkinetochore distance and loss of the centromeric protector of cohesion SGO2 in metaphase Two arrested (metII) eggs, as well every bit a ascension in the number of weakly fastened bivalents in meiosis I (MI) and lagging chromosomes at anaphase I. However, in that location were no MI errors in congression or biorientation. Instead, premature separation of dyads in meiosis II was the major segregation defect in aged eggs and these were associated with very depression levels of SGO2. These data prove that although considerable cohesion loss occurs during MI, its consequences are observed during meiosis II, when centromeric cohesion is needed to maintain dyad integrity." Chromosomes in the Porcine First Polar Body Possess Competence of Second Meiotic Division inside Enucleated MII Stage Oocytes [2] "These results demonstrate that chromosomes in PB1 can participate in normal pre-implantation embryonic development when injected into enucleated MII phase oocytes, and that tetraploid PA blastocysts are produced (although at a low proportion) when PB1 chromosomes are injected into intact MII stage oocytes." Bora regulates meiotic spindle assembly and prison cell cycle during mouse oocyte meiosis [11] "Bora is the binding partner of Aurora A, which is required for its activation and phosphorylation of Polo like kinase ane (Plk1), and is involved in the spindle assembly and progress of the cell cycle during mitosis. In this written report, we examined the expression, localization, and office of Bora during mouse oocyte meiosis. The expression level of Bora was increased during oocyte meiotic maturation, with an elevated level at metaphase. Immunofluorescence analysis showed that Bora was concentrated equally a dot presently after germinal vesicle breakdown (GVBD), associating commencement with the surrounding chromosomes and and then with the spindle throughout the oocyte meiotic maturation. Farther experiments confirmed that Bora co-localized with α-tubulin at prometaphase/metaphase, but dissociated from α-tubulin at anaphase/telophase."

Movies

A mouse oocyte undergoing meiosis spindle migration followed by start polar body extrusion and MII spindle positioning.[12] bluish - Hoechst staining of chromosomes. green - UtrCH-GFP was used to label cortical changes during spindle migration. The video shows that cytoplasmic streaming continues to the MII arrest stage to maintain the oocyte prepare of chromosomes/MII spindle in place close to the cortex. Frames are 11 min apart, and video length is 840 min. Bar, 20 µm.

A mouse spermatocyte undergoing meiosis prophase I. The chromosomal telomeres and synaptonemal complexes have been labelled to visualise chromosomal movement inside this single nucleus.[xiii]

Comparison of Meiosis/Mitosis

• After DNA replication ii nuclear (and jail cell) divisions required to produce haploid gametes
• Each diploid cell in meiosis produces 4 haploid cells (sperm) one haploid jail cell (egg)
• Each diploid cell mitosis produces 2 diploid cells

Meiosis Germ cell partition (haploid)

• Reductive division
• Generates haploid gametes (egg, sperm)
• Each genetically distinct from parent

• Genetic recombination (prophase ane)
  • Exchanges portions of chromosomes maternal/paternal homologous pairs
• Independent assortment of paternal chromosomes (meiosis ane)

Homologous chromosomes pairing unique to meiosis

• Each chromosome duplicated and exists every bit fastened sister chromatids before pairing occurs
• Genetic Recombination shown by chromosomes part red and part black
  • chromosome pairing in meiosis involves crossing-over between homologous chromosomes

Meiosis I and 2

• Meiosis I separates the pairs of homologous chromosomes, reduces the prison cell from diploid to haploid.
• Meiosis II separates each chromosome into two chromatids (chromosome behavior in meiosis II is like that of mitosis).

Links: Figure xiv.32. Comparison of meiosis and mitosis

Prophase I

prophase I

• The homologous chromosomes pair and commutation DNA to form recombinant chromosomes.
• Note - in oocyte development, from nascence until puberty oocytes are in "prophase I abort" at diplotene stage. This is important for sustaining the ovarian oocyte puddle and lutenizing hormone (LH) induces resumption of meiosis I.

Mouse early on meiotic prophase I stages[14]

Prophase I is further divided into five stages (phases):

Leptotene

• leptotene phase, leptonema; Greek, leptotene = "thin threads"
• the duplicated paired chromosome homologs condense.

Zygotene

• zygotene stage, zygonema, Greek, zygotene = "paired threads"
• homologous chromosomes go closely associated (synapsis) to form pairs of chromosomes consisting of four chromatids (tetrads).
• the synaptonemal complex begins to course betwixt the two sets of sister chromatids in each bivalent (the duplicated chromosome paired with its homologous duplicated chromosome).

Pachytene

• pachytene phase, pachynema; Greek, pachytene = "thick threads"
• crossing over betwixt pairs of homologous chromosomes (meiotic recombination or synapsis) to form chiasmata (grade between 2 nonsister chromatids at points where they have crossed over)
• synaptonemal complex is complete and can be stable for some time.
• Autosomal non-sister chromatids of homologous chromosomes can at present extensively exchange segments in regions of homology.
• Only small regions of non-paired sexual activity chromosomes collaborate
• Mutations that compromise meiotic recombination in male spermatocytes upshot in arrest and apoptosis at this phase.

Mouse meiosis pachytene^[15]

Diplotene

• diplotene stage, diplonema; Greek, diplonema = "ii threads"
• homologous chromosomes begin to separate but remain attached by chiasmata.
• synaptonemal complex degrades and the chromosomes separate from one another a small amount giving this appearance.
• It is possible that some chromosome uncoiling may also occur allowing some cistron transcription.
  • In the developing human ovary, oocytes remain at the diplotene phase from fetal life through postnatal childhood, until puberty when the lutenizing hormone (LH) surges stimulate the resumption of meiosis.

Diakinesis

• diakinesis phase; Greek, diakinesis = "moving through"
• homologous chromosomes continue to separate, and chiasmata movement to the ends of the chromosomes.
• prophase I ends and chromosomes at present recondense, transcription stops and the transition to metaphase occurs.

Prometaphase I

• Spindle apparatus formed, and chromosomes attached to spindle fibres by kinetochores.

Metaphase I

• Homologous pairs of chromosomes (bivalents) arranged as a double row forth the metaphase plate. The arrangement of the paired chromosomes with respect to the poles of the spindle apparatus is random along the metaphase plate. (This is a source of genetic variation through random assortment, as the paternal and maternal chromosomes in a homologous pair are similar but not identical. The number of possible arrangements is 2n, where northward is the number of chromosomes in a haploid prepare. Human beings have 23 different chromosomes, and then the number of possible combinations is 223, which is over viii 1000000.)

Anaphase I

• The homologous chromosomes in each bivalent are separated and move to the opposite poles of the jail cell.

Telophase I

• The chromosomes become diffuse and the nuclear membrane reforms.

Cytokinesis I

• Cellular cytoplasmic partition to form two new cells, followed by Meiosis 2.
• Note - in oocyte meiosis, the extrusion of the starting time polar trunk (ane Pb) indicates completion of the offset meiotic division.

Prophase II

• Chromosomes brainstorm to condense, nuclear membrane breaks downwards and spindle forms.

Metaphase Two

• Spindle fibres attach to chromosomes, chromosomes align in prison cell middle.

Anaphase Ii

• Chromosomes separate and move to the reverse poles of the cell.

Telophase 2

• Chromosomes reach spindle pole ends and the nuclear membrane reforms.

Cytokinesis

Cellular cytoplasmic division to form new cells.

Meiosis Sexual activity Differences

Female person (oogenesis)

• Meiosis initiated in one case in a finite population of cells
• 1 gamete produced / meiosis
• Completion of meiosis delayed for months or years
• Meiosis arrested at 1st meiotic prophase and reinitiated in a smaller population of cells
• Differentiation of gamete occurs while diploid in offset meiotic prophase
• All chromosomes exhibit equivalent transcription and recombination during meiotic prophase

Male (spermatogenesis)

• Meiosis initiated continuously in a mitotically dividing stem cell population
• 4 gametes produced / meiosis
• Meiosis completed in days or weeks
• Meiosis and differentiation proceed continuously without cell cycle arrest
• Differentiation of gamete occurs while haploid after meiosis ends

Sex chromosomes excluded from recombination and transcription during commencement meiotic prophase

Female Gametogenesis

In females, the full number of eggs ever to be produced are present in the newborn female.

1. All eggs are arrested at an early stage of the outset meiotic division as a primary oocyte (primordial follicle). Following purberty, during each menstrual cycle, pituitary gonadotrophin stimulates completion of meiosis i the twenty-four hour period before ovulation.
2. In meiosis 1, a diploid jail cell becomes 2 haploid (23 chromosomes) daughter cells, each chromosome has two chromatids. One prison cell becomes the secondary oocyte the other jail cell forms the first polar torso.
3. The secondary oocyte then commences meiosis ii which arrests at metaphase and will not go along without fertilization.
4. At fertilization meiosis 2 completes, forming a second polar body. Note that the first polar body may too undergo this procedure forming a third polar body.

Meiosis and Oogenesis[17]

Meiosis - divided into iii temporally distinct phases. Prophase - after DNA replication, homologous chromosomes (shown in cherry-red and blue) undergo pairing, synapsis and recombination, and arrest at the diplotene (dictyate) phase. Dictyate abort - oocytes remain in meiotic arrest until the female reaches maturity and the oocyte has completed an extensive period of growth following follicle formation. Divisions - luteinizing hormone (LH) surge that triggers ovulation as well causes resumption and completion of the first meiotic division in the periovulatory oocyte. The ovulated egg is arrested at 2nd meiotic metaphase, and anaphase onset and completion of meiosis II simply occur if the egg is fertilized. Oogenesis - complex involving 4 singled-out phases. Commitment to meiosis and meiotic initiation - occurs at GA eight–10 weeks in humans. Follicle formation - occurs during the second trimester in humans. Oocyte growth - occurs in the sexually mature female person under the control of paracrine and endocrine signals. Oocyte growth is idea to have approximately 85 days in humans and typically culminates in the ovulation of a single egg. Fertilization - of the ovulated egg results in the completion of the second meiotic division.

Oocyte Meiotic Spindles

Mammalian oocytes have no centrosomes, but still form spindles using many microtubule-organizing centres defective centrioles. (cells dividing by mitosis have 2 centrosomes to help form the mitotic spindle) PMID 17693257 Meiotic spindle is a microtubule construction but its relocation in the oocyte cytoplasm involves microfilaments, filamentous-actin structures nucleated by Formin-2 (Fmn2). PMID 19062278

Polar Body

First Polar Body^[12]

Human oocyte at metaphase II showing polar trunk at 12 o'clock position.

The breakdown of the germinal vesicle indicates a resumption of meiosis and the extrusion of the beginning polar body (i Pb) indicates completion of the first meiotic division in human oocytes. The polar body is a minor cytoplasmic exclusion body formed to enclose the backlog DNA formed during the oocyte (egg) meiosis and following sperm fertilization. At that place are 2-3 polar bodies derived from the oocyte present in the zygote, the number is dependent upon whether polar body 1 (the first polar trunk formed during meiosis 1) divides during meiosis 2. This exclusion body contains the backlog DNA from the reductive partitioning (the 2nd and third polar bodies are formed from meiosis 2 at fertilization). These polar bodies do not contribute to the future genetic complement of the zygote, embryo or fetus.

Recent inquiry in some species suggest that the infinite formed by the peripheral polar trunk (between the oocyte and the zona pellucia) can influence the site of spermatozoa fertilization.

Assisted reproductive techniques involving intracytoplasmic sperm injection (ICSI) have looked at the "quality" of the polar body and constitute that the morphology is related to mature oocyte viability and has the potential to predict oocyte fertilization rates and pregnancy accomplishment.^{[eighteen] [19]}

• Polar Body Electron Micrographs

• 

  First Polar Torso cortical granules

• 

  Commencement Polar Torso chromosomes

• 

  First Polar Body microtubules

• 

  Second Polar Trunk chromatin

• 

  Second Polar Body cytoplasmic bridge

Links: Category:Polar Torso

Female Abnormalities

Trisomy 21 female karyotype

Meiotic non-disjunction resulting in aneuploidy, nigh are embryonic lethal and not seen. The potential for genetic abnormalities increment with maternal historic period.

• Autosomal chromosome aneuploidy
  • Trisomy 21 - Down syndrome
  • Trisomy 18 - Edwards syndrome
  • Trisomy thirteen - Patau syndrome

• Sexual activity chromosome aneuploidy
  • Monosomy Ten - Turner's Syndrome
  • trisomy X - Triple-Ten syndrome
  • 47 XXY - Klinefelter's Syndrome

Male Gametogenesis

In males, sperm continues to be generated throughout life from a stem cell population in the testis. Spermatozoa maturation involves ii processes meiosis and spermiogenesis

The higher up figure compares meiosis to the female (the polar bodies accept been removed and labelling updated).

• 

  Historic testis drawing

• 

  Adult Seminiferous tubule showing spermatozoa developmental stages

• 

  Seminiferous tubule cross-section and supporting cells

• 

  Human being spermatozoa

Human Spermatozoa Development

• Spermatogenesis procedure of spermatagonia mature into spermatazoa (sperm).
• Continuously throughout life occurs in the seminiferous tubules in the male gonad- testis (plural testes).
• At puberty spermatagonia activate and proliferate (mitosis).
• about 48 days from entering meiosis until morphologically mature spermatozoa
• about 64 days to complete spermatogenesis, depending reproduction time of spermatogonia
• follicle stimulating hormone (FSH) - stimulates the spermatogenic epithelium
• luteinizing-hormone (LH) - stimulates testosterone product past Leydig cells

Mature human spermatozoa threescore µm long, actively motile divided into 3 main regions (head, neck and tail) head - (flattened, 5 µm long past iii µm broad) the nucleus and acrosome. Posterior part of nuclear membrane forms the basal plate. cervix - (1 µm) attached to basal plate, transverse oriented centriole, contains ix segmented columns of fibrous material, continue as outer dense fibres in tail. tail - iii parts a heart piece, main piece and end slice eye piece - (v µm long) axonema and dense fibres surrounded by mitochondria chief piece - (45 µm long) gristly sheath interconnected by regularly spaced circumferential hoops cease piece - (5 µm long) axonema surrounded by small amount of cytoplasm and plasma membrane

Links: Spermatozoa Development

Puberty

• In humans at puberty, hormonal and morphological changes occur inside the gonad and other systems (secondary sex characteristics).
• Within the testis the immature Sertoli cells cease to proliferate and differentiate.
• Spermatogonium proliferate and spermatogenesis begins.
• It takes near 70 days for cells to mature from the diploid spermatogonium to a primary spermatocyte.
• This maturation occurs in waves along the seminiferous tubules.

Links: Puberty

Ejeculate

Azoospermia - Non-obstructive azoospermia (NOA) and Obstructive azoospermia (OA)

• release of spermatozoa and accessory gland secretions from the male person genital tract (iii.5 ml)
• 200-600 million sperm, by volume less than ten % spermatozoa
• Accessory Gland secretions - 60 % seminal vesicle, 30 % prostate and 10 % bulbourethral

Male person Abnormalities

• Oligospermia - (Low Sperm Count) less than 20 million sperm after 72 hour forbearance from sexual activity
• Azoospermia - (Absent Sperm) blockage of duct network
• Immotile Cilia Syndrome - lack of sperm motility

Meiosis in Other Species

• Ocean urchin - oocytes complete meiosis earlier being shed.
• Starfish - oocytes only complete meiosis upon hormonal stimulation.

Abnormalities

Meiotic Nondisjunction

• Occurs when homologues neglect to divide during meiotic sectionalization I or II
• For instance trisomy 21 (Downwardly Syndrome) caused past an extra copy of chromosome 21

Links: trisomy 21 | Nondisjunction

Chromosomal Translocations

• Philadelphia chromosome
• Chronic myelogenous leukemia
  • Piece of Chr9 exchanged with Chr22 Generates truncated abl

Overstimulates cell production

References

1. ↑ ^{ane.0 1.1} Sakakibara Y, Hashimoto S, Nakaoka Y, Kouznetsova A, Höög C & Kitajima TS. (2015). Bivalent separation into univalents precedes historic period-related meiosis I errors in oocytes. Nat Commun , 6, 7550. PMID: 26130582 DOI.
2. ↑ ^{2.0 ii.ane} Lin T, Diao YF, Kang JW, Lee JE, Kim DK & Jin DI. (2013). Chromosomes in the porcine showtime polar body possess competence of second meiotic segmentation within enucleated MII stage oocytes. PLoS One , 8, e82766. PMID: 24312673 DOI.
3. ↑ Jan SZ, Jongejan A, Korver CM, van Daalen SKM, van Pelt AMM, Repping S & Hamer G. (2018). Distinct prophase abort mechanisms in human male meiosis. Development , 145, . PMID: 29540502 DOI.
4. ↑ Duan Ten & Lord's day SC. (2018). Actin cytoskeleton dynamics in mammalian oocyte meiosis. Biol. Reprod. , , . PMID: 30010726 DOI.
5. ↑ Wang S, Hassold T, Hunt P, White MA, Zickler D, Kleckner N & Zhang Fifty. (2017). Inefficient Crossover Maturation Underlies Elevated Aneuploidy in Human Female Meiosis. Cell , 168, 977-989.e17. PMID: 28262352 DOI.
6. ↑ Ren H, Ferguson Yard, Kirkpatrick G, Vinning T, Grub Five & Ma South. (2016). Contradistinct Crossover Distribution and Frequency in Spermatocytes of Infertile Men with Azoospermia. PLoS One , 11, e0156817. PMID: 27273078 DOI.
7. ↑ Mirzaghaderi G & Hörandl E. (2016). The development of meiotic sexual activity and its alternatives. Proc. Biol. Sci. , 283, . PMID: 27605505 DOI.
8. ↑ Bury L, Coelho PA & Glover DM. (2016). From Meiosis to Mitosis: The Astonishing Flexibility of Cell Partition Mechanisms in Early Mammalian Development. Curr. Superlative. Dev. Biol. , 120, 125-71. PMID: 27475851 DOI.
9. ↑ Royo H, Seitz H, ElInati Eastward, Peters AH, Stadler MB & Turner JM. (2015). Silencing of X-Linked MicroRNAs by Meiotic Sex Chromosome Inactivation. PLoS Genet. , 11, e1005461. PMID: 26509798 DOI.
10. ↑ Yun Y, Lane SI & Jones KT. (2014). Premature dyad separation in meiosis II is the major segregation mistake with maternal age in mouse oocytes. Evolution , 141, 199-208. PMID: 24346700 DOI.
11. ↑ Zhai R, Yuan YF, Zhao Y, Liu XM, Zhen YH, Yang FF, Wang L, Huang CZ, Cao J & Huo LJ. (2013). Bora regulates meiotic spindle assembly and cell wheel during mouse oocyte meiosis. Mol. Reprod. Dev. , 80, 474-87. PMID: 23610072 DOI.
12. ↑ ^{12.0 12.1} Yi Thou, Rubinstein B, Unruh JR, Guo F, Slaughter BD & Li R. (2013). Sequential actin-based pushing forces bulldoze meiosis I chromosome migration and symmetry breaking in oocytes. J. Cell Biol. , 200, 567-76. PMID: 23439682 DOI.
13. ↑ Shibuya H, Morimoto A & Watanabe Y. (2014). The dissection of meiotic chromosome movement in mice using an in vivo electroporation technique. PLoS Genet. , 10, e1004821. PMID: 25502938 DOI.
14. ↑ Boku T, Nakane Y, Komada H, Nakagawa M, Hirozane Due north, Hioki Yard & Yamamoto M. (1991). [Prognostic factors of "pm" gastric cancer]. Nihon Geka Gakkai Zasshi , 92, 17-23. PMID: 2014022
15. ↑ Pacheco Southward, Marcet-Ortega Thousand, Lange J, Jasin G, Keeney Due south & Roig I. (2015). The ATM signaling cascade promotes recombination-dependent pachytene abort in mouse spermatocytes. PLoS Genet. , xi, e1005017. PMID: 25768017 DOI.
16. ↑ Xu XL, Ma West, Zhu YB, Wang C, Wang BY, An N, An 50, Liu Y, Wu ZH & Tian JH. (2012). The microtubule-associated protein ASPM regulates spindle assembly and meiotic progression in mouse oocytes. PLoS I , 7, e49303. PMID: 23152892 DOI.
17. ↑ Nagaoka SI, Hassold TJ & Hunt PA. (2012). Human aneuploidy: mechanisms and new insights into an historic period-old trouble. Nat. Rev. Genet. , 13, 493-504. PMID: 22705668 DOI.
18. ↑ Ebner T, Yaman C, Moser Grand, Sommergruber Yard, Feichtinger O & Tews G. (2000). Prognostic value of first polar body morphology on fertilization charge per unit and embryo quality in intracytoplasmic sperm injection. Hum. Reprod. , 15, 427-30. PMID: 10655316
19. ↑ Younis JS, Radin O, Izhaki I & Ben-Ami M. (2009). Does offset polar torso morphology predict oocyte performance during ICSI handling?. J. Aid. Reprod. Genet. , 26, 561-seven. PMID: 19960239 DOI.

Textbooks

• MBoC - Sperm | MBoC - Highly simplified drawing of a cross-section of a seminiferous tubule in a mammalian testis | MBoC - Cytoplasmic bridges in developing sperm cells and their precursors

Podcasts

• Biosights 18 March 2013 - Breaking egg symmetry

Reviews

Greaney J, Wei Z & Homer H. (2017). Regulation of chromosome segregation in oocytes and the cellular basis for female person meiotic errors. Hum. Reprod. Update , , . PMID: 29244163 DOI.

Brar GA & Amon A. (2008). Emerging roles for centromeres in meiosis I chromosome segregation. Nat. Rev. Genet. , 9, 899-910. PMID: 18981989 DOI.

Articles

Zelazowski MJ, Sandoval M, Paniker Fifty, Hamilton HM, Han J, Gribbell MA, Kang R & Cole F. (2017). Age-Dependent Alterations in Meiotic Recombination Crusade Chromosome Segregation Errors in Spermatocytes. Cell , 171, 601-614.e13. PMID: 28942922 DOI.

Ren H, Ferguson One thousand, Kirkpatrick M, Vinning T, Chow V & Ma Southward. (2016). Contradistinct Crossover Distribution and Frequency in Spermatocytes of Infertile Men with Azoospermia. PLoS 1 , 11, e0156817. PMID: 27273078 DOI.

Wang Southward, Kleckner Northward & Zhang Fifty. (2017). Crossover maturation inefficiency and aneuploidy in human female meiosis. Cell Cycle , sixteen, 1017-1019. PMID: 28471715 DOI.

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Additional Images

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  Meiotic prophase I stages

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  Chromosome connections in meiosis

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  Kinetochore attachment to the spindle and chromosome cohesion in mitosis and meiosis

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  Human testis NANOG expression

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  Adult worm hermaphrodite gonad arm

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  Mouse oocyte microtubule-associated protein

Terms

Cell Sectionalization Terms (aggrandize to view)
meiosis | mitosis anaphase - (Greek, ana = up, once again) Mitosis term referring to the fourth phase, where the paired chromatids now separate and migrate to spindle poles. This is followed by telophase. anaphase A - Mitosis term referring to the part of anaphase during which the chromosomes move. anaphase B - Mitosis term referring to the part of anaphase during which the poles of the mitotic spindle motility autonomously. aneuploidy - (aneuploid) term used to describe an abnormal number of chromosomes mainly (90%) due to chromosome malsegregation mechanisms in maternal meiosis I. aster - (Latin, aster = star) star-similar object visible in nearly dividing eukaryotic cells contains the microtubule organizing heart. astral microtubule - spindle apparatus microtubule (MT) originating from the centrosome which does not connect to a kinetochore. These microtubules but be during mitosis, the other spindle types are polar and kinetochore microtubules. autosomal inheritance - term used in hereditary diseases which means that the disease is due to a DNA error in 1 of the 22 chromosome pairs that are not sex chromosomes. Both boys and girls can then inherit this fault. If the error is in a sex chromosome, the inheritance is said to be sexual practice-linked. bivalent - (tetrad) a pair of homologous chromosomes physically held together by at to the lowest degree one Deoxyribonucleic acid crossover. bouquet stage - meiosis term for when in prophase transition to the zygotene stage, the chromosome telomeres attachment to the inner nuclear envelope and form a cluster. This occurs earlier the onset of homologous pairing and synapsis. The name comes from the chromosomes resembling a "bouquet of flowers". diploid - (Greek, di = double + ploion = vessel) having two sets of chromosomes (2n), this is the normal euploidy state for all human cells, other than gametes that are haploid (n, a single gear up of chromosomes). diplotene stage- (diplotene phase, diplonema; Greek, diplonema = "two threads") meiotic stage seen during prophase I, the chromosomes separate from i another a small amount giving this appearance. In the developing human ovary, oocytes remain at the diplotene stage from fetal life through postnatal babyhood, until puberty when the lutenizing hormone (LH) surges stimulate the resumption of meiosis. Prophase I, is divided into 5 stages (leptotene, zygotene, pachytene, diplotene, diakinesis) based upon changes associated with the synaptonemal complex structure that forms between two pairs of homologous chromosomes. euploidy - the normal genome chromosomal gear up (n, 2n, 3n) or complement for a species, in humans this is diploid (2n). The other classes of numerical chromosomal abnormalities include aneuploidy, polyploidy and mixoploidy. FUCCI - Acronym for Fluorescence Ubiquitination Cell Cycle Indicator a molecular tool for identifying the stage in the cell cycle. In G0/G1 cells express a red fluorescent protein and Southward/G2/M cells express a dark-green fluorescent protein. (More than? Tooth Development Movie) haploid - (Greek, haploos = single) Having a single fix of chromosomes (n) as in mature germ/sexual practice cells (oocyte, spermatozoa) following reductive prison cell partition by meiosis. Normally cells are diploid, containing 2 sets of chromosomes. Ploidy refers to the number of sets of chromosomes in the nucleus of a prison cell. heteroplasmy - presence of more than one type of organellar genome. In humans this can refer to variations in the mitochondrial DNA (mtDNA). (More than? PMID 26281784) homologous chromosomes - meiosis term for the ii matching (maternal and one paternal) chromosomes that align during meiosis I. homologous recombination - meiosis term when DNA of homologous chromosomes is covalently exchanged to produce chromosomes with new allele combinations, and also links homologous chromosomes with each other to class a bivalent human genome - Dna within the 23 nucleus chromosome pairs and the cytoplasmic mitochondrial Deoxyribonucleic acid. kinetochore - the protein construction formed on chromatids where the spindle kinetochore microtubules attach during cell division. kinetochore microtubule - spindle appliance microtubule (MT) that attaches to the chromosome kinetochore by its plus cease, the other spindle types are astral and polar microtubules. kinesin - a microtubule (MT) motor poly peptide that exists in many isoforms and virtually movement towards the MT positive finish. Different isoforms have different functions within the spindle apparatus. PMID 20109570 meiosis - reductive cell division required to produce germ cells (oocyte, spermatozoa) and for sexual reproduction. Notation that only spermatozoa complete meiosis earlier fertilisation. Chromosome number is reduced from diploid to haploid, during this process maternal and paternal genetic material are exchanged. All other non-germ cells in the body divide past mitosis. (More? Meiosis | Spermatozoa Development | Oocyte Evolution | Week one) meiosis I - (MI) the first part of meiosis resulting in separation of homologous chromosomes, in humans producing two haploid cells (N chromosomes, 23), a reductional segmentation. meiosis 2 - (MII) the second part of meiosis. In male man spermatogenesis, producing of iv haploid cells (23 chromosomes, 1N) from the ii haploid cells (23 chromosomes, 1N), each of the chromosomes consisting of two sis chromatids produced in meiosis I. In female homo oogenesis, only a single haploid cell (23 chromosomes, 1N) is produced. Meiosis Two: Prophase Ii - Metaphase II - Anaphase Two - Telophase II. meiotic silencing of unsynapsed chromatin - (MSUC) an aneuploidy protective machinery for subsequent generations, during meiosis where chromosomes are silenced that fail to pair with their homologous partners. merotelic kinetochore - cell partition abnormality in chromosomal attachment that occurs when a single kinetochore is attached to microtubules arising from both spindle poles. Normal chromosomal attachment in early mitosis, is by only i of the two sis kinetochores attached to spindle microtubules (monotelic attachment) later sis kinetochores attach to microtubules arising from opposite spindle poles (amphitelic zipper). metaphase - mitosis term referring to the third stage where mitotic spindle kinetochore microtubules align chromosomes in one midpoint aeroplane. Metaphase ends when sister kinetochores divide. Originally based on light microscopy of living cells and electron microscopy of fixed and stained cells. A light microscope assay called a "metaphase spread" was originally used to detect chromosomal abnormalities in cells. Mitosis Phases: prophase - prometaphase - metaphase - anaphase - telophase metaphase spread - In mitosis using light microscope assay originally used to discover chromosomal abnormalities in cells, as chromosomes are only visible during cell division. microfilament - (MF) cytoskeleton filament normally required for cytoplasmic intracellular send, motility and cell shape. Named by the actin monomers assembling into the smallest in cross-section of the three filament systems (microtubules and intermediate filaments). This system is disassembled and reassembled as the contractile band for cytokinesis (cytoplasm division) post-obit jail cell division mitosis and meiosis. microtubule - (MT) cytoskeleton filament usually required for cytoplasmic intracellular transport and movement. Named past the tubulin monomers assembling into "tubes", and are the largest in cross-section of the 3 filament systems (microfilaments and intermediate filaments). This system is disassembled and reassembled every bit the spindle apparatus during cell segmentation. mitochondrial Dna - (mtDNA) multiple copies of a small circular Deoxyribonucleic acid molecule located within the mitochondria matrix. In humans xvi,568 bp in length containing 37 genes, originally inherited only from the oocyte (maternal inheritance). mitosis - (M stage) The normal division of all cells, except germ cells, where chromosome number is maintained (diploid). In germ cell division (oocyte, spermatozoa) meiosis is a modified course of this division resulting in reduction in genetic content (haploid). Mitosis, division of the nucleus, is followed by cytokinesis the segmentation of the cell cytoplasm and the cytoplasmic contents. cytokinesis overlaps with telophase. p - chromosome brusque arm (possibly French, petit) and used along with chromosome and band number to indicate genes located on this arm of the chromosome. The chromosome long arm is identified as q (possibly French, tall) chosen as adjacent letter in alphabet afterwards p. These chromosomal arms are merely seen when the chromosome is folded for cell sectionalisation. polar body - a small cytoplasmic exclusion body containing the excess DNA formed during the oocyte meiosis wheel and following spermatozoa fertilization. polar microtubule - spindle appliance microtubule (MT) that tin can arise from either pole and overlap at the spindle midzone. This interdigitating construction consisting of antiparallel microtubules is responsible for pushing the poles of the spindle autonomously. The other spindle types are astral and kinetochore microtubules. prometaphase - (Greek, pro = before) mitosis term referring to the second stage, when the nuclear envelope breaks down into vesicles. Microtubules and then extend from the centrosomes at the spindle poles (ends) and accomplish the chromosomes. This is followed past metaphase. pronuclear fusion - (Greek, pro = before) the procedure of the fusion of the two haploid nuclear structures (pronuclei) contributed from the spermatazoa and oocyte to course the showtime diploid nucleus cell. Can likewise be chosen "fusion of pronuclei". pronucleus - (Greek, pro = before; plural, pronuclei) the two haploid nuclei or nuclear structures containing the genetic material from the spermatozoa and the oocyte. These two haploid nuclei will fuse together to grade the first diploid nucleus cell, the zygote. Therefore the nuclear structures that exist "before the nucleus", the plural term is pronuclei. prophase - (Greek, pro = before) - mitosis term referring to the first phase, when the diffusely stained chromatin resolves into discrete chromosomes, each consisting of ii chromatids joined together at the centromere. prophase I - meiosis term refers to the first stage of meiosis I, which together with meiosis 2 results in the reductive cell sectionalisation only occurring gametes. Prophase can be further divided into a number of stages: leptotene zygotene, pachytene, diplotene, diakinesis. q - chromosome long arm (perhaps French, tall), the next letter in alphabet after p, and used along with chromosome and band number to indicate genes located on this arm of the chromosome. The chromosome short arm is identified as p (perhaps French, petit). These chromosomal arms are only seen when the chromosome is folded for jail cell division. S phase - during interphase of cell cycle where DNA is duplicated prior to second growth period (G2 stage) that is followed by mitosis (M stage). synapsis - (syndesis) meiosis term for the pairing of ii homologous chromosomes that occurs during prophase I. synaptonemal complex - meiosis term for a protein construction essential for synapsis of homologous chromosomes. (proteins SCP3 and SCP1). telomere - region found at each end of the chromosome and involved in cellular ageing and the capacity for segmentation. The regions consist of repeated sequences protecting the ends of chromosomes and harbour Dna repair proteins. In the absence of the enzyme telomerase, these regions shorten during each cell partition and becoming critically short, cell senescence occurs. telophase - mitosis term referring to the fifth stage, where the vesicles of the nuclear envelope reform around the girl cells, the nucleoli reappear and the chromosomes unfold to let gene expression to begin. This stage overlaps with cytokinesis, the division of the cell cytoplasm. telomerase - the enzyme that maintains the chromosome stop length, the telomeres, involved in cellular ageing and the chapters for division. Absenteeism of telomerase activity leads to the chromosome ends shorten during each cell division, becoming critically short and cell senescence then occurs. tetrad - (bivalent) a pair of homologous chromosomes physically held together by at to the lowest degree one Dna crossover.
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Cite this page: Hill, G.A. (2022, May 18) Embryology Cell Division - Meiosis. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Cell_Division_-_Meiosis

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Source: https://embryology.med.unsw.edu.au/embryology/index.php/Cell_Division_-_Meiosis

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