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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...
Karyotyping01:17

Karyotyping

Overview
Karyotyping01:17

Karyotyping

Overview
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: May 17, 2026

FISH for Pre-implantation Genetic Diagnosis
07:34

FISH for Pre-implantation Genetic Diagnosis

Published on: February 23, 2011

The trisomy 18 syndrome.

Anna Cereda1, John C Carey

  • 1Ambulatorio Genetica Clinica Pediatrica, Clinica Pediatrica Universita Milano Bicocca, Fondazione MBBM A.O, S, Gerardo Monza, Italy.

Orphanet Journal of Rare Diseases
|October 24, 2012
PubMed
Summary

Edwards syndrome (trisomy 18) is a common chromosomal disorder affecting 1 in 6,000 newborns. This condition presents with multiple anomalies, significant growth deficiency, and high infant mortality, requiring specialized care.

Area of Science:

  • Genetics
  • Medical Genetics
  • Pediatrics

Background:

  • Trisomy 18 syndrome, or Edwards syndrome, is the second most common autosomal trisomy.
  • It is characterized by an extra chromosome 18, leading to a complex pattern of anomalies.
  • Prevalence is higher than live-born rates due to fetal loss and termination.

Purpose of the Study:

  • To describe the clinical presentation and management challenges of trisomy 18.
  • To highlight the high mortality rates and common causes of death.
  • To emphasize the need for diligent health supervision in affected infants.

Main Methods:

  • Review of clinical features and epidemiological data for trisomy 18.
  • Analysis of common anomalies, growth deficiencies, and mortality causes.

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Chromosome Preparation From Cultured Cells
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Last Updated: May 17, 2026

FISH for Pre-implantation Genetic Diagnosis
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Published on: February 23, 2011

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

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  • Discussion of diagnostic approaches including prenatal screening.

    • Main Results:

    • Trisomy 18 presents with major and minor anomalies, growth deficiency, and high neonatal mortality.
    • Congenital heart defects and kidney anomalies are frequent.
    • Survival rates show approximately 50% live beyond 1 week and 5-10% beyond 1 year.

    Conclusions:

    • Management of trisomy 18 is complex due to severe clinical presentation and high mortality.
    • Upper airway obstruction is a significant, often underestimated, cause of death.
    • Diligent health supervision, especially in the first year, is crucial for affected infants.