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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.

Karyotyping

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...

Neurulation

Neurulation

Neurulation is the embryological process which forms the precursors of the central nervous system and occurs after gastrulation has established the three primary cell layers of the embryo: ectoderm, mesoderm, and endoderm. In humans, the majority of this system is formed via primary neurulation, in which the central portion of the ectoderm—originally appearing as a flat sheet of cells—folds upwards and inwards, sealing off to form a hollow neural tube. As development proceeds, the anterior...

Cohesins

Cohesins

Cohesin protein complexes are a molecular glue that holds two sister chromatids together. They play an important role both in mitosis and meiosis. In mitosis, all cohesin complexes present on the chromosomes are removed before the start of the anaphase stage.
Cohesin complexes in Meiotic Division
Meiosis involves two distinct rounds of chromosomal segregation and cell divisions— Meiosis I followed by Meiosis II – producing four daughter cells. Meiosis I includes the separation of homologous...

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...

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A Novel Strategy Combining Array-CGH, Whole-exome Sequencing and In Utero Electroporation in Rodents to Identify Causative Genes for Brain Malformations

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Holoprosencephaly: An update on cytogenetic abnormalities.

Claude Bendavid¹, Valérie Dupé, Lucie Rochard

¹Institut National de la Santé et de la Recherche Médicale, Rennes, France.

American Journal of Medical Genetics. Part C, Seminars in Medical Genetics

|January 28, 2010

Summary

Holoprosencephaly (HPE) is a brain defect caused by failed midline cleavage. Advanced genomic techniques reveal new chromosomal anomalies, aiding the identification of critical HPE regions and genes.

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Area of Science:

Developmental biology
Genetics
Clinical genetics

Background:

Holoprosencephaly (HPE) is the most common forebrain and midface developmental defect, resulting from early embryonic midline cleavage failure.
While genetic factors are implicated, known gene mutations explain only 25% of isolated HPE cases, highlighting the need for broader genomic investigation.

Purpose of the Study:

To update the catalog of cytogenetic anomalies associated with Holoprosencephaly (HPE).
To map subtelomeric and interstitial deletions in HPE patients using advanced techniques.
To facilitate the delineation of minimal critical HPE loci for identifying novel HPE-associated genes.

Main Methods:

Review and compilation of cytogenetic data from HPE patients.
Characterization of chromosomal aberrations using karyotyping, subtelomeric multiplex ligation-dependent probe amplification (MLPA), and microarray-based comparative genomic hybridization (array CGH).
Mapping of identified subtelomeric and interstitial deletions.

Main Results:

A comprehensive map of cytogenetic anomalies in HPE, including subtelomeric and interstitial deletions, has been compiled.
High-resolution techniques like MLPA and array CGH have improved the detection of chromosomal aberrations in HPE.
The study consolidates recurrent genomic imbalances linked to HPE.

Conclusions:

The updated map of genomic imbalances provides a crucial resource for understanding HPE etiology.
Continued accumulation of data on recurrent genomic imbalances will refine minimal critical HPE loci.
This refined understanding is essential for the discovery of new genes involved in Holoprosencephaly.