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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...
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...
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.
Gene Conversion02:08

Gene Conversion

Other than maintaining genome stability via DNA repair, homologous recombination plays an important role in diversifying the genome. In fact, the recombination of sequences forms the molecular basis of genomic evolution. Random and non-random permutations of genomic sequences create a library of new amalgamated sequences. These newly formed genomes can determine the fitness and survival of cells. In bacteria, homologous and non-homologous types of recombination lead to the evolution of new...

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Related Experiment Video

Updated: Jun 20, 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

Broad-scale recombination patterns underlying proper disjunction in humans.

Adi Fledel-Alon1, Daniel J Wilson, Karl Broman

  • 1Department of Human Genetics, University of Chicago, Chicago, Illinois, United States of America.

Plos Genetics
|September 19, 2009
PubMed
Summary
This summary is machine-generated.

Human meiosis requires at least one crossover per chromosome for proper segregation. Additional crossovers correlate with chromosome length, with potential backup mechanisms for chromosome 21 and non-interfering double crossovers observed.

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Preparation of Meiotic Chromosome Spreads from Zebrafish Spermatocytes
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Preparation of Meiotic Chromosome Spreads from Zebrafish Spermatocytes

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Last Updated: Jun 20, 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

Frequency and Distribution of Crossovers in Caenorhabditis elegans Meiosis by SNP Genotyping using Real-time PCR
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Frequency and Distribution of Crossovers in Caenorhabditis elegans Meiosis by SNP Genotyping using Real-time PCR

Published on: July 11, 2025

Preparation of Meiotic Chromosome Spreads from Zebrafish Spermatocytes
08:46

Preparation of Meiotic Chromosome Spreads from Zebrafish Spermatocytes

Published on: March 3, 2020

Area of Science:

  • Human genetics
  • Molecular biology
  • Cellular processes

Background:

  • Recombination is crucial for accurate chromosome segregation during human meiosis.
  • The precise regulation and scale of recombination constraints remain incompletely understood.

Purpose of the Study:

  • To investigate the nature and stringency of constraints on human recombination.
  • To analyze crossover patterns in transmissions to viable, non-trisomic offspring.

Main Methods:

  • Utilized dense genotyping data from a large cohort of human pedigrees.
  • Examined crossover patterns in relation to chromosome structure and transmission outcomes.

Main Results:

  • Evidence supports a requirement for one chiasma per chromosome, not per arm, for ensuring proper disjunction.
  • Additional chiasmata occur proportionally to physical chromosome length.
  • Chromosome 21 may be correctly segregated in females even without a chiasma, suggesting a backup mechanism.
  • Observed closely spaced double crossovers, indicative of a pathway independent of crossover interference.

Conclusions:

  • Multiple mechanisms regulate crossover distribution during human meiosis.
  • These regulatory mechanisms are critical for ensuring proper chromosome disjunction.
  • The findings shed light on the complex control of genetic recombination in humans.