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Meiosis I

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...

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...

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.

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...

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In Vitro Modeling of Down Syndrome Neurogenesis Using Human-Induced Pluripotent Stem Cells

In Vitro Modeling of Down Syndrome Neurogenesis Using Human-Induced Pluripotent Stem Cells

Published on: March 7, 2025

Specific entities affecting the craniocervical region: Down's syndrome.

Arnold H Menezes¹

¹Department of Neurosurgery, University of Iowa Hospitals and Clinics, 200 Hawkins Drive, 1824 JPP, Iowa City, IA 52242, USA. arnold-menezes@uiowa.edu

Child'S Nervous System : Chns : Official Journal of the International Society for Pediatric Neurosurgery

|April 19, 2008

Summary

Children with Down syndrome and other skeletal dysplasias often have craniocervical junction abnormalities. Early recognition through imaging is crucial for appropriate management and to avoid poor surgical outcomes.

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Area of Science:

Pediatric Orthopedics
Radiology
Genetics

Background:

Ligamentous laxities and bony abnormalities are common in pediatric patients with Down syndrome, os odontoideum, achondroplasia, osteogenesis imperfecta, and basilar invagination.
These conditions significantly impact the craniocervical junction, necessitating high clinical suspicion.

Purpose of the Study:

To highlight the importance of imaging the craniocervical junction in children with specific genetic and skeletal conditions.
To emphasize the need for understanding the underlying pathology for effective surgical management.

Main Methods:

Review of imaging findings at the craniocervical junction.
Correlation of imaging findings with specific pediatric conditions.

Main Results:

Abnormalities of the craniocervical junction are frequently observed in children with the discussed conditions.
Imaging plays a critical role in identifying these abnormalities.

Conclusions:

Understanding the specific pathologies associated with Down syndrome, os odontoideum, achondroplasia, osteogenesis imperfecta, and basilar invagination is vital.
Inadequate understanding has led to adverse surgical outcomes in managing these complex pediatric cases.