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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...
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.
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 II02:02

Meiosis II

Meiosis II entails cell division and segregation of the sister chromatids, resulting in the production of four unique haploid gametes. The steps for meiosis II are similar to mitosis, except that meiosis II occurs in haploid cells, whereas mitosis occurs in diploid cells.
The timing and cell division patterns of meiosis differ between males and females. In male meiosis, the centrosomes are part of the formation of the meiotic spindle. However, in oocytes, including that of humans, Drosophila,...

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Related Experiment Video

Updated: Jul 10, 2026

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

Dizygotic twinning.

Chantal Hoekstra1, Zhen Zhen Zhao, Cornelius B Lambalk

  • 1Department of Biological Psychology, VU University Amsterdam, van der Boechorststraat 1, 1081 BT Amsterdam, The Netherlands. c.hoekstra@psy.vu.nl

Human Reproduction Update
|November 21, 2007
PubMed
Summary

Genetic and environmental factors influence dizygotic (DZ) twin rates, which vary geographically. While maternal factors like age and family history play a role, specific gene mutations are only partly responsible for DZ twinning.

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Model Surgical Training: Skills Acquisition in Fetoscopic Laser Photocoagulation of Monochorionic Diamniotic Twin Placenta Using Realistic Simulators
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Model Surgical Training: Skills Acquisition in Fetoscopic Laser Photocoagulation of Monochorionic Diamniotic Twin Placenta Using Realistic Simulators

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

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Related Experiment Videos

Last Updated: Jul 10, 2026

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

Model Surgical Training: Skills Acquisition in Fetoscopic Laser Photocoagulation of Monochorionic Diamniotic Twin Placenta Using Realistic Simulators
09:51

Model Surgical Training: Skills Acquisition in Fetoscopic Laser Photocoagulation of Monochorionic Diamniotic Twin Placenta Using Realistic Simulators

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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

Area of Science:

  • Reproductive biology
  • Human genetics
  • Maternal health

Background:

  • Spontaneous dizygotic (DZ) twinning is a complex trait influenced by genetics and environment.
  • Twinning frequency varies geographically and over time, primarily due to differences in DZ twinning rates.
  • Maternal factors including genetic history, advanced maternal age, high parity, taller stature, and higher BMI are associated with increased DZ twinning risk.

Purpose of the Study:

  • To explore the multifactorial influences on spontaneous dizygotic twinning.
  • To identify genetic and environmental contributors to variations in twinning rates.

Main Methods:

  • Review of existing literature on twinning rates and associated factors.
  • Analysis of maternal characteristics and family history in relation to twinning.
  • Genetic association studies investigating specific gene mutations.

Main Results:

  • DZ twinning rates exhibit significant variation, unlike the stable monozygotic twinning rate.
  • Maternal genetic history, advanced age, parity, height, and BMI are confirmed risk factors for DZ twinning.
  • Mutations in the growth differentiation factor 9 (GDF9) gene are more frequent in mothers of DZ twins, but account for a small portion of the genetic influence.

Conclusions:

  • Both genetic predisposition and environmental factors significantly contribute to dizygotic twinning.
  • While certain maternal characteristics and rare gene mutations are implicated, the full genetic basis for DZ twinning remains largely unexplained.