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Meiosis II

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 II

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...

Meiosis II

Meiosis II

Meiosis I

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...

Meiosis I

Meiosis I

Meiosis is a carefully orchestrated set of cell divisions, the goal of which—in humans—is to produce haploid sperm or eggs, each containing half the number of chromosomes present in somatic cells elsewhere in the body. Meiosis I is the first such division, and involves several key steps, among them: condensation of replicated chromosomes in diploid cells; the pairing of homologous chromosomes and their exchange of information; and finally, the separation of homologous chromosomes by...

Meiosis I

Meiosis I

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Related Experiment Video

Updated: Apr 30, 2026

Using Fluorescence In Situ Hybridization FISH to Monitor the State of Arm Cohesion in Prometaphase and Metaphase I Drosophila Oocytes

Using Fluorescence In Situ Hybridization FISH to Monitor the State of Arm Cohesion in Prometaphase and Metaphase I Drosophila Oocytes

Published on: December 6, 2017

Age-related decrease of meiotic cohesins in human oocytes.

Makiko Tsutsumi¹, Reiko Fujiwara¹, Haruki Nishizawa²

¹Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi, Japan.

|May 9, 2014

Summary

This summary is machine-generated.

Maternal age increases oocyte aneuploidy risk. This study finds reduced meiotic cohesin proteins in older women, suggesting impaired cohesion leads to chromosome segregation errors and birth defects.

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Meiotic Spindle Assessment in Mouse Oocytes by siRNA-mediated Silencing

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Published on: October 11, 2015

Area of Science:

Reproductive biology
Genetics
Cell biology

Background:

Fetal chromosome aneuploidy contributes to pregnancy loss and birth defects.
Oocyte aneuploidy frequency rises with maternal age.
Cohesin complexes are crucial for accurate meiotic chromosome segregation.

Purpose of the Study:

To investigate cohesin levels in human and mouse oocytes across different age groups.
To explore the link between age-related cohesin decline and oocyte aneuploidy.

Main Methods:

Immunofluorescence analysis of ovarian sections from various age groups of humans and mice.
Quantification of meiotic cohesin subunits (REC8, SMC1B) and mitotic cohesin subunit (SMC1A).

Main Results:

Meiosis-specific cohesin subunits (REC8, SMC1B) significantly decreased in oocytes from women aged 40+ compared to younger women.
Similar age-related declines in meiotic cohesins were observed in mice.
Mitotic cohesin SMC1A was present in human oocytes but scarce in mice, with a slight age-related increase in mice.

Conclusions:

Age-related decreases in meiotic cohesin subunits impair sister chromatid cohesion in oocytes.
This impairment leads to increased chromosome segregation errors, contributing to aneuploidy and adverse pregnancy outcomes.
Coordinated action of mitotic and meiotic cohesins may maintain cohesion over time in humans.