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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...
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 vs. Mitosis02:57

Meiosis vs. Mitosis

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...
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.

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Related Experiment Video

Updated: Jul 8, 2026

In Vitro Modeling of Down Syndrome Neurogenesis Using Human-Induced Pluripotent Stem Cells
06:38

In Vitro Modeling of Down Syndrome Neurogenesis Using Human-Induced Pluripotent Stem Cells

Published on: March 7, 2025

Is Down syndrome a disappearing birth defect?

Veronica R Collins1, Evelyne E Muggli, Merilyn Riley

  • 1Public Health Genetics, Murdoch Childrens Research Institute, Royal Children's Hospital, Victoria, Australia. veronica.collins@mcri.edu.au

The Journal of Pediatrics
|December 25, 2007
PubMed
Summary

The prevalence of Down syndrome (DS) increased in Victoria, Australia, between 1986 and 2004, particularly in women under 35. Prenatal diagnosis rates rose significantly, highlighting the need for ongoing support services for individuals with DS.

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Generation of Induced Pluripotent Stem Cells from Turner Syndrome (45XO) Fetal Cells for Downstream Modelling of Neurological Deficits Associated with the Syndrome
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Generation of Induced Pluripotent Stem Cells from Turner Syndrome (45XO) Fetal Cells for Downstream Modelling of Neurological Deficits Associated with the Syndrome

Published on: December 4, 2021

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Last Updated: Jul 8, 2026

In Vitro Modeling of Down Syndrome Neurogenesis Using Human-Induced Pluripotent Stem Cells
06:38

In Vitro Modeling of Down Syndrome Neurogenesis Using Human-Induced Pluripotent Stem Cells

Published on: March 7, 2025

Generation of Induced Pluripotent Stem Cells from Turner Syndrome (45XO) Fetal Cells for Downstream Modelling of Neurological Deficits Associated with the Syndrome
09:39

Generation of Induced Pluripotent Stem Cells from Turner Syndrome (45XO) Fetal Cells for Downstream Modelling of Neurological Deficits Associated with the Syndrome

Published on: December 4, 2021

Area of Science:

  • Medical Science
  • Genetics
  • Public Health

Background:

  • Down syndrome (DS) is a genetic disorder associated with intellectual disability and developmental delays.
  • Understanding trends in DS prevalence is crucial for public health planning and resource allocation.

Purpose of the Study:

  • To analyze the prevalence of Down syndrome (DS) in Victoria, Australia, from 1986 to 2004.
  • To identify demographic and temporal trends in DS diagnoses.

Main Methods:

  • Data linkage between the Victorian Birth Defects Register and the Prenatal Diagnosis Database.
  • Calculation of annual total and birth prevalence estimates for DS.
  • Presentation of data using 3-year moving averages.

Main Results:

  • Total DS cases increased from 113 (1986) to 188 (2004).
  • Prevalence in women under 35 rose from 10/10,000 to 12.5/10,000; in older women, it increased from 70/10,000 to 90/10,000.
  • Prenatal diagnosis proportion increased from 3% to 60% in younger women.

Conclusions:

  • The study highlights an increasing trend in Down syndrome prevalence.
  • Findings underscore the ongoing need for resources and support systems for individuals with DS and their families.