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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 I03:09

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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...
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Overview
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Meiosis vs. Mitosis02:57

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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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Nondisjunction01:21

Nondisjunction

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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...
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Related Experiment Video

Updated: Jan 3, 2026

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

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Down syndrome.

Michael S Rafii1, Alexander M Kleschevnikov2, Mariko Sawa2

  • 1Department of Neurology, Keck School of Medicine of the University of Southern California, San Diego, CA, United States.

Handbook of Clinical Neurology
|November 23, 2019
PubMed
Summary
This summary is machine-generated.

Down syndrome (DS) affects the brain, causing issues like intellectual disability and dementia. Research is crucial as people with DS live longer, to better understand and manage these neurologic conditions.

Keywords:
AgingAlzheimer's diseaseDementiaDown syndromeTrisomy 21

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Area of Science:

  • Neurology
  • Genetics
  • Gerontology

Background:

  • Down syndrome (DS), or Trisomy 21, is the most common human chromosomal disorder.
  • Neurologic conditions such as intellectual disability, sleep apnea, seizures, behavioral issues, and dementia are common in DS.
  • Increased lifespan in individuals with DS necessitates research into age-related neurologic conditions.

Purpose of the Study:

  • To address the scarcity of information regarding neurologic phenotypes in aging individuals with DS.
  • To clarify the risks and understanding of dementia in adults with Down syndrome.
  • To discuss the biologic bases and management strategies for neurologic conditions in DS.

Main Methods:

  • Literature review of neurologic phenotypes in Down syndrome.
  • Analysis of current understanding of biologic bases for DS-associated conditions.
  • Discussion of management strategies for neurologic conditions in DS.

Main Results:

  • Down syndrome presents with a spectrum of neurologic phenotypes.
  • Alzheimer's disease (AD) is a significant concern for aging individuals with DS.
  • There is a need for clearer data on dementia risk in the DS population.

Conclusions:

  • Further research is essential to understand the long-term neurologic health of individuals with DS.
  • Accurate information on dementia risk is vital for the DS community's well-being and care.
  • Understanding the biologic underpinnings of DS neurologic conditions can improve management.