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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

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...
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.
Genetic Screens02:46

Genetic Screens

Genetic screens are tools used to identify genes and mutations responsible for phenotypes of interest. Genetic screens help identify individuals or a group of people at risk of developing  genetic diseases and help them with early intervention, targeted therapy, and reproductive options.
Forward genetic screens
Forward or “classical” genetic screens involve creating random mutations in an organism’s DNA using radiation, mutagens, or insertion of additional bases, which result in visible changes...
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...
Nondisjunction01:21

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...

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Related Experiment Video

Updated: Jun 28, 2026

Semiconductor Sequencing for Preimplantation Genetic Testing for Aneuploidy
09:03

Semiconductor Sequencing for Preimplantation Genetic Testing for Aneuploidy

Published on: August 25, 2019

Down syndrome screening in multiple pregnancies.

Alexandra Matias1, Nuno Montenegro, Isaac Blickstein

  • 1Department of Obstetrics and Gynecology, Faculty of Medicine, Porto, University Hospital of S. João, Porto, Portugal. almatias@mail.telepac.pt

Obstetrics and Gynecology Clinics of North America
|January 13, 2005
PubMed
Summary
This summary is machine-generated.

First and second trimester screening for twin pregnancies is effective using ultrasound and biochemistry. Nuchal translucency measurements are key for counseling high-risk twin pregnancies regarding invasive testing.

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Pre-Implantation Genetic Testing for Aneuploidy on a Semiconductor Based Next-Generation Sequencing Platform
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Chromosome Screening of Human Preimplantation Embryos by Using Spent Culture Medium: Sample Collection and Chromosomal Ploidy Analysis
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Area of Science:

  • Maternal-fetal medicine
  • Prenatal screening
  • Twin pregnancy diagnostics

Background:

  • First or second trimester screening for twin pregnancies is feasible and effective.
  • Biochemical screening in multiples is less sensitive and has questionable validity.
  • Nuchal translucency (NT) is a primary factor for counseling in high-risk twin pregnancies.

Purpose of the Study:

  • To evaluate the efficacy of first and second trimester screening in twin pregnancies.
  • To provide guidance on risk assessment and counseling for invasive testing in twin gestations.
  • To address the specific challenges of biochemical and NT screening in multiples.

Main Methods:

  • Utilizing a combination of ultrasound and maternal serum biochemistry in the first trimester.
  • Employing maternal serum biochemistry in the second trimester.
  • Calculating pregnancy-specific risks for dizygotic twins by summing individual risks.
  • Calculating risk for monozygotic twins using the geometric mean of NT measurements.

Main Results:

  • Screening in twin pregnancies is feasible and efficacious.
  • Biochemical screening in multiples has reduced sensitivity.
  • NT measurements are crucial for counseling, with higher false-positive rates than in singletons.
  • Specific risk calculation methods are proposed for dizygotic and monozygotic twins.

Conclusions:

  • First and second trimester screening methods are viable for twin pregnancies.
  • Nuchal translucency measurement is the predominant factor for counseling in high-risk twin pregnancies.
  • Special considerations are needed for biochemical screening and NT false-positive rates in twin gestations.