World Library  
Flag as Inappropriate
Email this Article

Chromosome abnormalities

Article Id: WHEBN0017072567
Reproduction Date:

Title: Chromosome abnormalities  
Author: World Heritage Encyclopedia
Language: English
Subject: Oncogene, Trisomy, Deletion (genetics), Aneuploidy, Chromosomal translocation, Chromosomal inversion, Ring chromosome, 48, XXXX, Ring chromosome 20 syndrome, Isodicentric 15
Collection:
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Chromosome abnormalities


A chromosome anomaly, abnormality or aberration is a missing, extra, or irregular portion of chromosomal DNA.[1] It can be from an atypical number of chromosomes or a structural abnormality in one or more chromosomes. A karyotype refers to a full set of chromosomes from an individual which can be compared to a "normal" karyotype for the species via genetic testing. A chromosome anomaly may be detected or confirmed in this manner. Chromosome anomalies usually occur when there is an error in cell division following meiosis or mitosis. There are many types of chromosome anomalies. They can be organized into two basic groups, numerical and structural anomalies.

Numerical disorders

This is called aneuploidy (an abnormal number of chromosomes), and occurs when an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy, tetrasomy, etc.).

In humans an example of a condition caused by a numerical anomaly is Down Syndrome, also known as Trisomy 21 (an individual with Down Syndrome has three copies of chromosome 21, rather than two). Trisomy has been determined to be a function of maternal age.

An example of monosomy is Turner Syndrome, where the individual is born with only one sex chromosome, an X.

Structural abnormalities

When the chromosome's structure is altered, this can take several forms:

  • Deletions: A portion of the chromosome is missing or deleted. Known disorders in humans include Wolf-Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4; and Jacobsen syndrome, also called the terminal 11q deletion disorder.
  • Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material. Known human disorders include Charcot-Marie-Tooth disease type 1A which may be caused by duplication of the gene encoding peripheral myelin protein 22 (PMP22) on chromosome 17.
  • Translocations: A portion of one chromosome is transferred to another chromosome. There are two main types of translocations:
  • Inversions: A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted.
  • Insertions: A portion of one chromosome has been deleted from its normal place and inserted into another chromosome.
  • Rings: A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without loss of genetic material.
  • Isochromosome: Formed by the mirror image copy of a chromosome segment including the centromere.

Chromosome instability syndromes are a group of disorders characterized by chromosomal instability and breakage. They often lead to an increased tendency to develop certain types of malignancies.

Inheritance

Most chromosome abnormalities occur as an accident in the egg or sperm, and therefore the anomaly is present in every cell of the body. Some anomalies, however, can happen after conception, resulting in Mosaicism (where some cells have the anomaly and some do not). Chromosome anomalies can be inherited from a parent or be "de novo". This is why chromosome studies are often performed on parents when a child is found to have an anomaly. If the parents do not possess the abnormality it was not initially inherited; however it may be transmitted to subsequent generations.

See also

References

External links

  • Medical Subject Headings (MeSH)
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.