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Related Concept Videos

Meiosis I01:49

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 a...
Nondisjunction01:29

Nondisjunction

During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed sister chromatid separation during meiosis II. In some species, notably plants, nondisjunction can result in an organism with an entire additional set of chromosomes, which is called polyploidy. In humans, nondisjunction can occur during male or female gametogenesis and the resulting gametes possess one too many or one too few chromosomes.
Cohesins02:20

Cohesins

Cohesin protein complexes are a molecular glue that holds two sister chromatids together. They play an important role both in mitosis and meiosis. In mitosis, all cohesin complexes present on the chromosomes are removed before the start of the anaphase stage.
Cohesin complexes in Meiotic Division
Meiosis involves two distinct rounds of chromosomal segregation and cell divisions— Meiosis I followed by Meiosis II – producing four daughter cells. Meiosis I includes the separation of homologous...
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...
Nondisjunction01:29

Nondisjunction

During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed sister chromatid separation during meiosis II. In some species, notably plants, nondisjunction can result in an organism with an entire additional set of chromosomes, which is called polyploidy. In humans, nondisjunction can occur during male or female gametogenesis and the resulting gametes possess one too many or one too few chromosomes.
Nondisjunction01:21

Nondisjunction

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 sister...

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Related Experiment Video

Updated: May 11, 2026

Studying Age-dependent Genomic Instability using the S. cerevisiae Chronological Lifespan Model
08:46

Studying Age-dependent Genomic Instability using the S. cerevisiae Chronological Lifespan Model

Published on: September 29, 2011

Cohesin and the maternal age effect.

William D Gilliland1, R Scott Hawley

  • 1Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA.

Cell
|November 5, 2005
PubMed
Summary

Maternal age increases nondisjunction errors during meiosis. A study found that a mutation in the SMC1beta protein in mice causes age-dependent meiotic defects, suggesting a similar mechanism in humans.

Area of Science:

  • Reproductive biology
  • Genetics
  • Cell biology

Background:

  • Chromosome nondisjunction in human oocytes rises with maternal age, causing conditions like Down syndrome.
  • Meiosis is a critical cell division process for sexual reproduction.

Purpose of the Study:

  • To investigate the role of the meiosis-specific cohesin protein SMC1beta in age-dependent meiotic errors.
  • To explore potential mechanisms underlying the maternal age effect on chromosome segregation.

Main Methods:

  • The study utilized a mouse model with a mutation in the SMC1beta gene.
  • Researchers analyzed meiotic progression and chromosome segregation in oocytes from these mice.

Main Results:

  • Mice with the SMC1beta mutation displayed age-dependent defects in meiosis.

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Combining Magnetic Sorting of Mother Cells and Fluctuation Tests to Analyze Genome Instability During Mitotic Cell Aging in Saccharomyces cerevisiae
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Combining Magnetic Sorting of Mother Cells and Fluctuation Tests to Analyze Genome Instability During Mitotic Cell Aging in Saccharomyces cerevisiae

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Using Fluorescence In Situ Hybridization (FISH) to Monitor the State of Arm Cohesion in Prometaphase and Metaphase I Drosophila Oocytes
12:46

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

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Last Updated: May 11, 2026

Studying Age-dependent Genomic Instability using the S. cerevisiae Chronological Lifespan Model
08:46

Studying Age-dependent Genomic Instability using the S. cerevisiae Chronological Lifespan Model

Published on: September 29, 2011

Combining Magnetic Sorting of Mother Cells and Fluctuation Tests to Analyze Genome Instability During Mitotic Cell Aging in Saccharomyces cerevisiae
11:08

Combining Magnetic Sorting of Mother Cells and Fluctuation Tests to Analyze Genome Instability During Mitotic Cell Aging in Saccharomyces cerevisiae

Published on: October 16, 2014

Using Fluorescence In Situ Hybridization (FISH) to Monitor the State of Arm Cohesion in Prometaphase and Metaphase I Drosophila Oocytes
12:46

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

  • These defects mimicked the errors observed in oocytes from older human mothers.
  • The findings suggest a link between SMC1beta function and age-related meiotic errors.

    • Conclusions:

    • An age-dependent loss of function in SMC1beta may contribute to the maternal age effect in humans.
    • SMC1beta or related proteins are implicated in maintaining meiotic fidelity with advancing maternal age.