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Related Concept Videos

Karyotyping

Karyotyping

Karyotyping

Karyotyping

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...

Nondisjunction

Nondisjunction

X and Y Chromosomes

X and Y Chromosomes

Among mammals, the gender of an organism is determined by the sex chromosomes. Humans have two sex chromosomes, X and Y. Every human diploid cell has 22 pairs of autosomes and one pair of sex chromosomes. A human female has two X chromosomes, while a male has one X chromosome and one Y chromosome.
The germline cells such as egg and sperm cells carry only half the number of chromosomes, i.e., 22 autosomes and one sex chromosome. All eggs have an X chromosome, while sperm cells can carry an X or...

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Related Experiment Video

Updated: Apr 20, 2026

Chromosome Preparation From Cultured Cells

Chromosome Preparation From Cultured Cells

Published on: January 28, 2014

Adults with Chromosome 18 Abnormalities.

Bridgette Soileau¹, Minire Hasi, Courtney Sebold

¹Department of Pediatrics, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA.

Journal of Genetic Counseling

|November 19, 2014

Summary

Adults with chromosome 18 abnormalities show improved educational outcomes and some independent living capabilities. This longitudinal study offers crucial data for families navigating rare chromosome conditions and provides guidance on potential life trajectories.

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Area of Science:

Genetics
Developmental Biology
Clinical Genetics

Background:

Chromosome abnormalities, such as 18q-, 18p-, Tetrasomy 18p, and Ring 18, present diagnostic challenges.
Families of children with rare chromosome conditions often lack longitudinal data for future planning.
Anticipatory guidance is difficult due to limited long-term outcome information for these individuals.

Purpose of the Study:

To describe the lifespan, educational attainment, living situation, and behavioral phenotype of adults with chromosome 18 abnormalities.
To provide crucial data for counseling families regarding potential outcomes.
To offer insights into the long-term prognosis for individuals with chromosome 18 conditions.

Main Methods:

Longitudinal study collecting annual data from 483 individuals with chromosome 18 abnormalities.
Data collection includes living arrangements, educational level, employment status, executive functioning, and behavioral skills.
Analysis of mortality data, including cause and age at death, for deceased participants.

Main Results:

Educational attainment is generally higher than previously reported, with some individuals pursuing post-high school education.
A minority of participants over 18 are capable of independent living.
Mortality data is presented, with a majority of deaths linked to TCF4 gene deletions or unbalanced rearrangements.
Executive function and behavioral phenotypes are detailed for the cohort.

Conclusions:

Longitudinal data reveals improved educational outcomes and potential for independent living in adults with chromosome 18 abnormalities.
The study provides critical insights into the long-term trajectory of these rare genetic conditions.
Findings are essential for informing families about the diverse range of outcomes and supporting informed decision-making.