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Related Concept Videos

Crossing Over01:30

Crossing Over

Crossing over is the exchange of genetic information between homologous chromosomes during prophase I of meiosis I. Genetic recombination gives rise to allelic diversity in the newly formed daughter cells. In humans, crossing over produces genetically distinct haploid egg and sperm cells that undergo fertilization to produce unique offspring. Before cell division starts, the germ cell’s chromosome(s) undergo duplication in the S phase of the cell cycle. As the cells enter prophase I, duplicated...
Crossing Over01:34

Crossing Over

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 called synapsis.
In order to...
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...
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...
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.

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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

Complex chromosomal rearrangements: origin and meiotic behavior.

F Pellestor1, T Anahory, G Lefort

  • 1INSERM U847, IRB, CHRU Montpellier, Montpellier I University, Montpellier, France. f-pellestor@chu-montpellier.fr

Human Reproduction Update
|April 14, 2011
PubMed
Summary

Complex chromosomal rearrangements (CCRs) are rare but clinically significant genetic events. Advanced molecular techniques reveal their intricate nature and formation mechanisms, though genetic counseling for carriers remains challenging.

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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

Chromosome Preparation From Cultured Cells
07:42

Chromosome Preparation From Cultured Cells

Published on: January 28, 2014

Rapid Analysis of Chromosome Aberrations in Mouse B Lymphocytes by PNA-FISH
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Published on: August 19, 2014

Area of Science:

  • Genetics
  • Molecular Biology
  • Human Health

Background:

  • Complex chromosomal rearrangements (CCRs) involve at least three breakpoints on two or more chromosomes.
  • CCRs can lead to diverse phenotypes, including infertility and congenital abnormalities, and can be de novo or familial.
  • Previous studies suggested CCRs were more complex than initially assumed, with elusive formation mechanisms.

Purpose of the Study:

  • To summarize current knowledge on CCR formation and meiotic behavior.
  • To highlight the complexity of CCRs at chromosomal and genomic levels.
  • To address important aspects of CCRs.

Main Methods:

  • A comprehensive PubMed search was conducted.
  • Published data on CCRs were reviewed.
  • Focus was placed on chromosomal and genomic complexity.

Main Results:

  • Molecular techniques increasingly reveal the complexity of CCRs.
  • Breakpoint sequence analysis identified insertions, deletions, inversions, and recombination events.
  • New models propose replication-based mechanisms and specific sequence elements for CCR formation.

Conclusions:

  • Understanding of CCR genesis is growing, but they remain unique, complex events.
  • The meiotic behavior of CCRs is being re-evaluated in light of new molecular data.
  • Genetic and reproductive counseling for CCR carriers presents ongoing challenges.