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Related Concept Videos

Meiosis I01:49

Meiosis I

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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...
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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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Meiosis II01:57

Meiosis II

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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...
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Crossing Over01:34

Crossing Over

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Unlike mitosis, meiosis aims for genetic diversity in its creation of haploid gametes. Dividing germ cells first begin this process in prophase I, where each chromosome—replicated in S phase—is now composed of two sister chromatids (identical copies) joined centrally.
The homologous pairs of sister chromosomes—one from the maternal and one from the paternal genome—then begin to align alongside each other lengthwise, matching corresponding DNA positions in a process...
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Nondisjunction01:29

Nondisjunction

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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.
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What is Meiosis?01:36

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.
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Super-Resolution Microscopy of the Synaptonemal Complex Within the Caenorhabditis elegans Germline
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Super-Resolution Microscopy of the Synaptonemal Complex Within the Caenorhabditis elegans Germline

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Meiotic Chromosome Structure, the Synaptonemal Complex, and Infertility.

Ian R Adams1, Owen R Davies2

  • 1Medical Research Council (MRC) Human Genetics Unit, MRC Institute of Genetics and Cancer, University of Edinburgh, Edinburgh, United Kingdom;

Annual Review of Genomics and Human Genetics
|May 9, 2023
PubMed
Summary

Mutations in synaptonemal complex (SC) genes disrupt meiosis, leading to infertility. Understanding these genetic defects reveals how SC protein variations cause pathogenic dominant-negative effects, impacting fertility.

Keywords:
azoospermiafertilitymeiosisprimary ovarian failurerecurrent pregnancy losssynaptonemal complex

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Area of Science:

  • Cell Biology
  • Genetics
  • Reproductive Biology

Background:

  • Meiosis requires homologous chromosome synapsis, facilitated by the synaptonemal complex (SC).
  • The mammalian SC is a protein structure essential for chromosome pairing, crossover formation, and segregation.
  • SC dysfunction due to gene mutations is linked to human infertility.

Purpose of the Study:

  • To elucidate the molecular mechanisms linking SC gene mutations to human infertility.
  • To integrate structural SC data with genetic findings from mouse and human studies.
  • To identify patterns of mutation susceptibility in different SC proteins.

Main Methods:

  • Structural analysis of human SC proteins.
  • Integration of mouse and human genetic data.
  • Analysis of mutation types and their effects on SC function.

Main Results:

  • SC protein mutations can impair synapsis, crossover, and segregation.
  • Different SC proteins exhibit distinct mutation susceptibilities.
  • Minor genetic variants can act as dominant-negative mutations, causing infertility in heterozygotes.

Conclusions:

  • SC structure and function are critical for successful meiosis and fertility.
  • Understanding SC mutation mechanisms provides insights into infertility causes.
  • Targeted genetic analysis of SC proteins can identify infertility risk factors.