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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...
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.
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...
Karyotyping01:17

Karyotyping

Describing the number and physical features of chromosomes can reveal abnormalities that underlie genetic diseases. This description is facilitated by special staining techniques that produce a particular banding pattern on each chromosome. State-of-the-art techniques make this approach even more powerful, enabling the detection of individual genes that cause disease.A Simple Chromosome Staining Technique Provides Valuable Scientific InsightSome genetic diseases can be detected by looking at...

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Related Experiment Video

Updated: Jun 21, 2026

Accurate and Simple Evaluation of Vascular Anastomoses in Monochorionic Placenta using Colored Dye
09:52

Accurate and Simple Evaluation of Vascular Anastomoses in Monochorionic Placenta using Colored Dye

Published on: September 5, 2011

Down syndrome in monochorionic twins.

I L Sin1, T Y T Tan

  • 1Raffles Women's Centre, Raffles Hospital, 585 North Bridge Road, #12-00, Singapore.

Singapore Medical Journal
|August 1, 2009
PubMed
Summary
This summary is machine-generated.

This case report details a rare prenatal diagnosis of Down syndrome in monochorionic twins. Early screening and ultrasound identified the condition, leading to termination.

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Guide Wire Assisted Catheterization and Colored Dye Injection for Vascular Mapping of Monochorionic Twin Placentas
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Guide Wire Assisted Catheterization and Colored Dye Injection for Vascular Mapping of Monochorionic Twin Placentas

Published on: September 5, 2011

Related Experiment Videos

Last Updated: Jun 21, 2026

Accurate and Simple Evaluation of Vascular Anastomoses in Monochorionic Placenta using Colored Dye
09:52

Accurate and Simple Evaluation of Vascular Anastomoses in Monochorionic Placenta using Colored Dye

Published on: September 5, 2011

Guide Wire Assisted Catheterization and Colored Dye Injection for Vascular Mapping of Monochorionic Twin Placentas
09:04

Guide Wire Assisted Catheterization and Colored Dye Injection for Vascular Mapping of Monochorionic Twin Placentas

Published on: September 5, 2011

Area of Science:

  • Maternal-Fetal Medicine
  • Prenatal Diagnostics
  • Genetics

Background:

  • Monochorionic twins share a placenta, increasing risks for complications.
  • Down syndrome (Trisomy 21) is a genetic disorder typically screened for during pregnancy.
  • Prenatal diagnosis of Down syndrome in monochorionic twins is infrequently documented.

Observation:

  • Maternal serum screening at 15 weeks indicated a high risk (>1:50) for Down syndrome.
  • Early ultrasonography confirmed a monochorionic twin pregnancy.
  • Amniocentesis on one twin sac at 17 weeks confirmed Down syndrome.

Findings:

  • A subsequent screening scan at 19 weeks revealed absent nasal bones in both twins.
  • This suggests potential concordance of Down syndrome in both fetuses.
  • The case highlights diagnostic challenges in multiple gestations.

Implications:

  • Early and accurate prenatal diagnosis is crucial for informed decision-making.
  • Monochorionic twin pregnancies require careful monitoring for specific genetic conditions.
  • Further research is needed on the incidence and presentation of Down syndrome in monochorionic twins.