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Related Concept Videos

Oogenesis02:07

Oogenesis

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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...
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Meiosis I03:09

Meiosis I

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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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Meiosis II02:02

Meiosis II

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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,...
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Nondisjunction01:21

Nondisjunction

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Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate correctly and move to the opposite poles of the cells. This produces daughter cells with abnormal chromosome numbers.  Nondisjunction is common during anaphase I or anaphase II of meiosis.  Mutations in synaptonemal complex proteins that attach homologous chromosomes increase the chances of nondisjunction in anaphase I of meiosis I. In contrast, mutations in topoisomerases and condensins that hold...
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Meiosis vs. Mitosis02:57

Meiosis vs. Mitosis

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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...
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What is Meiosis?01:34

What is Meiosis?

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Meiosis is the process by which diploid cells divide to produce haploid daughter cells. In humans, each diploid cell contains 46 chromosomes, half from the mother and half from the father. Following meiosis, the resulting haploid eggs or sperm only contain 23 chromosomes; however, each of these chromosomes contains a unique combination of parental information that results from the meiotic process of crossing over.
Although meiosis shares similarities with mitosis—both rely on microtubules...
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Updated: Oct 6, 2025

Using Mouse Oocytes to Assess Human Gene Function During Meiosis I
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Using Mouse Oocytes to Assess Human Gene Function During Meiosis I

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Next Generation Sequencing Detects Premeiotic Errors in Human Oocytes.

Harita Ghevaria1, Sioban SenGupta1, Roy Naja1

  • 1Preimplantation Genetics Group, Institute for Women's Health, University College London (UCL), London WC1E 6HX, UK.

International Journal of Molecular Sciences
|January 21, 2022
PubMed
Summary
This summary is machine-generated.

Premeiotic aneuploidy, a source of embryonic death, affects over 10% of human oocytes due to germinal mosaicism. This condition significantly increases the risk of aneuploid conceptions, regardless of maternal age.

Keywords:
human oocytesmeiosismetaphase II oocyte and first polar body complexnext generation sequencingpremeiotic aneuploidy

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Area of Science:

  • Reproductive Biology
  • Human Genetics
  • Developmental Biology

Background:

  • Autosomal aneuploidy is a primary cause of human embryonic and fetal mortality.
  • Errors during oogenesis (meiosis I or II) are the main contributors.
  • Germinal mosaicism, leading to premeiotic aneuploidy, is an underrecognized factor.

Purpose of the Study:

  • To independently investigate the incidence of premeiotic aneuploidy in unmanipulated human oocytes.
  • To validate findings from previous molecular cytogenetic studies.
  • To assess the impact of premeiotic aneuploidy on oocyte euploidy.

Main Methods:

  • Utilized next-generation sequencing (NGS) for analysis.
  • Examined a series of 140 unselected oocytes from 42 women.
  • Analyzed both immature (germinal vesicle, metaphase I) and mature (metaphase II) oocytes.

Main Results:

  • Confirmed premeiotic aneuploidy incidence exceeding 10% (11.4% in this study).
  • Identified 16 out of 140 oocytes (11.4%) with premeiotic aneuploidy.
  • Found higher aneuploidy rates in mature oocytes (21.4%) compared to immature ones (8.93%).
  • Observed both simple and complex chromosomal errors in aneuploid oocytes.

Conclusions:

  • Germinal mosaicism leading to premeiotic aneuploidy is a consistent finding in at least 10% of oocytes.
  • Premeiotic aneuploidy significantly elevates the risk of producing an aneuploid mature oocyte.
  • This finding may explain aneuploid conceptions in younger women, independent of maternal age.