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Nondisjunction

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...

Nondisjunction

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. Mitosis

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...

Cleavage and Blastulation

Cleavage and Blastulation

After a large-single-celled zygote is produced via fertilization, the process of cleavage occurs while zygotes travel through the uterine tube. Cleavage is a mitotic cell division that does not result in growth. With each round of successive cell division, daughter cells get increasingly smaller.

Oogenesis

Oogenesis

In human women, oogenesis produces one mature egg cell or ovum for every precursor cell that enters meiosis. This process differs in two unique ways from the equivalent procedure of spermatogenesis in males. First, meiotic divisions during oogenesis are asymmetric, meaning that a large oocyte (containing most of the cytoplasm) and minor polar body are produced as a result of meiosis I, and again following meiosis II. Since only oocytes will go on to form embryos if fertilized, this unequal...

Development of the Sexual Organs in the Embryo and Fetus

Development of the Sexual Organs in the Embryo and Fetus

Development of the reproductive organs in an embryo starts from a bipotential state. This means the early embryo can develop either male or female reproductive organs. The formation of these organs begins with the growth of gonadal ridges that arise from the intermediate mesoderm during the fifth week of development.
Near the gonadal ridges, two duct systems are present: the mesonephric ducts (Wolffian ducts) and paramesonephric ducts (Müllerian ducts). These ducts form the basis for the male...

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Related Experiment Video

Updated: Jul 3, 2026

Semiconductor Sequencing for Preimplantation Genetic Testing for Aneuploidy

Semiconductor Sequencing for Preimplantation Genetic Testing for Aneuploidy

Published on: August 25, 2019

Aneuploidy and early human embryo development.

Gayane Ambartsumyan¹, Amander T Clark

¹Department of Molecular Cell and Developmental Biology, University of California, Los Angeles, CA 90095, USA.

Human Molecular Genetics

|July 18, 2008

Summary

This summary is machine-generated.

Human embryonic development involves complex processes, but chromosomal abnormalities can lead to miscarriage. Human embryonic stem cells offer a new model for studying these early genetic events and understanding developmental errors.

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Using Mouse Oocytes to Assess Human Gene Function During Meiosis I

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Chromosome Screening of Human Preimplantation Embryos by Using Spent Culture Medium: Sample Collection and Chromosomal Ploidy Analysis

Chromosome Screening of Human Preimplantation Embryos by Using Spent Culture Medium: Sample Collection and Chromosomal Ploidy Analysis

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Last Updated: Jul 3, 2026

Semiconductor Sequencing for Preimplantation Genetic Testing for Aneuploidy

Semiconductor Sequencing for Preimplantation Genetic Testing for Aneuploidy

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Using Mouse Oocytes to Assess Human Gene Function During Meiosis I

Using Mouse Oocytes to Assess Human Gene Function During Meiosis I

Published on: April 10, 2018

Chromosome Screening of Human Preimplantation Embryos by Using Spent Culture Medium: Sample Collection and Chromosomal Ploidy Analysis

Chromosome Screening of Human Preimplantation Embryos by Using Spent Culture Medium: Sample Collection and Chromosomal Ploidy Analysis

Published on: September 7, 2021

Area of Science:

Reproductive biology
Developmental biology
Genetics

Background:

Human embryo development involves reprogramming, cell division, and genome activation.
Chromosomal abnormalities during early development are a significant cause of miscarriage and birth defects.
Studying human germ cell and embryo development has been historically challenging due to limited model systems.

Purpose of the Study:

To review literature on diagnosing chromosomal abnormalities in pre-implantation embryos.
To highlight the role of human embryonic stem cells as a model for genetic studies.
To explore the importance of oocyte provisions in early human embryonic genome maintenance.

Main Methods:

Literature review focusing on diagnosing chromosomal abnormalities.
Analysis of transcriptional data from human oocytes and embryos.
Examination of cell cycle and checkpoint requirements in early human embryos.

Main Results:

Human embryonic stem cells present a valuable model for studying pre-implantation pluripotent cells.
The human oocyte plays a crucial role in establishing and maintaining the embryonic genome.
Early human embryo programs, including aneuploid cell management, may paradoxically aid development while increasing miscarriage rates.

Conclusions:

Understanding early human embryonic genome management is key to addressing high miscarriage rates.
Human embryonic stem cells provide a promising avenue for genetic research in early development.
Further research into oocyte contributions and embryonic cell cycle regulation is warranted.