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Related Concept Videos

Meiosis vs. Mitosis02:57

Meiosis vs. Mitosis

Cell division is necessary for growth and reproduction in organisms. Mitosis aids cell growth and development by dividing somatic cells. In contrast, meiosis causes the division of germ cells and plays an essential role in sexual reproduction. Due to their unique functional requirements, mitosis and meiosis differ from each other in multiple aspects.
Before the start of mitosis and meiosis I, the cell synthesizes DNA, resulting in two homologous copies of each chromosome. DNA synthesis is...
Oogenesis02:07

Oogenesis

In human women, oogenesis produces one mature egg cell or ovum for every precursor cell that enters meiosis. This process differs in two unique ways from the equivalent procedure of spermatogenesis in males. First, meiotic divisions during oogenesis are asymmetric, meaning that a large oocyte (containing most of the cytoplasm) and minor polar body are produced as a result of meiosis I, and again following meiosis II. Since only oocytes will go on to form embryos if fertilized, this unequal...
Oogenesis01:22

Oogenesis

Oogenesis,  the process of developing egg cells (female gametes), occurs within the ovaries and is fundamental to female fertility. This sequence begins during fetal development when diploid oogonia in the developing ovaries undergo mitotic divisions to produce primary oocytes. By birth, these primary oocytes enter prophase I of meiosis but become arrested in this stage, remaining suspended until puberty.
Each primary oocyte is surrounded by a layer of pre-granulosa cells, forming what is known...
Meiosis II02:02

Meiosis II

Meiosis II entails cell division and segregation of the sister chromatids, resulting in the production of four unique haploid gametes. The steps for meiosis II are similar to mitosis, except that meiosis II occurs in haploid cells, whereas mitosis occurs in diploid cells.
The timing and cell division patterns of meiosis differ between males and females. In male meiosis, the centrosomes are part of the formation of the meiotic spindle. However, in oocytes, including that of humans, Drosophila,...
Meiosis II01:57

Meiosis II

Meiosis II is the second and final stage of meiosis. It relies on the haploid cells produced during meiosis I, each of which contain only 23 chromosomes—one from each homologous initial pair. Importantly, each chromosome in these cells is composed of two joined copies, and when these cells enter meiosis II, the goal is to separate such sister chromatids using the same microtubule-based network employed in other division processes. The result of meiosis II is two haploid cells, each containing...
Meiosis I03:09

Meiosis I

Meiosis is the division of a diploid cell into haploid cells forming sperm and eggs in animals through differentiation. Meiosis I is the first stage of meiosis, where the genetic recombination of homologous chromosomes and the reduction of the ploidy level by half occurs.
Prophase I is the most extended and complex step of meiosis I characterized by synapsis, chromosome pairing, and recombination of the homologous chromosomes. This process is facilitated by a proteinaceous structure called the...

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Related Experiment Video

Updated: Jun 2, 2026

Preparation of Meiotic Chromosome Spreads from Mouse Oocytes for Assessment of Synapsis and Recombination
09:24

Preparation of Meiotic Chromosome Spreads from Mouse Oocytes for Assessment of Synapsis and Recombination

Published on: July 18, 2025

Oocyte-specific differences in cell-cycle control create an innate susceptibility to meiotic errors.

So Iha Nagaoka1, Craig A Hodges, David F Albertini

  • 1School of Molecular Biosciences and Center for Reproductive Biology, Washington State University, Pullman, WA 99163, USA.

Current Biology : CB
|April 19, 2011
PubMed
Summary

Univalent chromosomes in female meiosis do not trigger cell cycle arrest, unlike in males. This study shows stable bipolar attachment of most chromosomes, not all, is needed for cell division, potentially explaining human aneuploidy.

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Meiotic Spindle Assessment in Mouse Oocytes by siRNA-mediated Silencing
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Evaluation of the Spindle Assembly Checkpoint Integrity in Mouse Oocytes
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Evaluation of the Spindle Assembly Checkpoint Integrity in Mouse Oocytes

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Last Updated: Jun 2, 2026

Preparation of Meiotic Chromosome Spreads from Mouse Oocytes for Assessment of Synapsis and Recombination
09:24

Preparation of Meiotic Chromosome Spreads from Mouse Oocytes for Assessment of Synapsis and Recombination

Published on: July 18, 2025

Meiotic Spindle Assessment in Mouse Oocytes by siRNA-mediated Silencing
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Meiotic Spindle Assessment in Mouse Oocytes by siRNA-mediated Silencing

Published on: October 11, 2015

Evaluation of the Spindle Assembly Checkpoint Integrity in Mouse Oocytes
10:09

Evaluation of the Spindle Assembly Checkpoint Integrity in Mouse Oocytes

Published on: September 13, 2022

Area of Science:

  • Cell Biology
  • Genetics
  • Reproductive Biology

Background:

  • Meiosis I (MI) chromosome segregation relies on crossovers and kinetochore attachments.
  • Univalent chromosomes, arising from recombination failure, pose a challenge to accurate segregation.
  • Mammalian oocytes, unlike male cells, do not arrest in response to univalents during MI.

Purpose of the Study:

  • To investigate the spindle assembly checkpoint (SAC) response to univalent chromosomes in mammalian oocytes.
  • To determine the requirements for MI spindle stabilization and anaphase onset.
  • To explore the mechanisms underlying aneuploidy in human oocytes.

Main Methods:

  • Utilized Mlh1 mutant mice to study meiotic progression.
  • Analyzed chromosome behavior and spindle assembly checkpoint activation.
  • Assessed the relationship between chromosome attachment and anaphase onset.

Main Results:

  • Demonstrated that metaphase alignment is not essential for anaphase onset in oocytes.
  • Provided evidence that stable bipolar attachment of a critical mass of chromosomes stabilizes the MI spindle.
  • Showed that univalents do not necessarily trigger cell cycle arrest in oocytes.

Conclusions:

  • The oocyte SAC may have reduced stringency towards aberrant chromosome configurations.
  • Stable bipolar attachment of most, but not all, chromosomes is crucial for successful meiosis I.
  • Differences in SAC regulation may contribute to human oocyte error proneness and age-related aneuploidy.