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Encyclopedia > Chromosome abnormality
The three major single chromosome mutations; deletion (1), duplication (2) and inversion (3).
The three major single chromosome mutations; deletion (1), duplication (2) and inversion (3).
The two major two chromosome mutations; insertion (1) and translocation (2).
The two major two chromosome mutations; insertion (1) and translocation (2).

A chromosome abnormality reflects an abnormality of chromosome number or structure. Chromosome abnormalities usually occur when there is an error in cell division following meiosis or mitosis. There are many types of chromosome abnormalities. However, they can be organized into two basic groups, numerical and structural abnormalities. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File links Size of this preview: 431 × 599 pixel Image in higher resolution (616 × 856 pixel, file size: 19 KB, MIME type: image/png) By Richard Wheeler (Zephyris) 2007. ... Image File history File links Size of this preview: 431 × 599 pixel Image in higher resolution (616 × 856 pixel, file size: 19 KB, MIME type: image/png) By Richard Wheeler (Zephyris) 2007. ... This does not adequately cite its references or sources. ... Not to be confused with miosis. ... Mitosis divides genetic information during cell division. ...

Contents

Numerical abnormalities

Main article: Aneuploidy

When an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy). An example of a condition caused by numerical abnormalities is Down Syndrome, also known as Trisomy 21 (an individual with Down Syndrome has three copies of chromosome 21, rather than two). Turner Syndrome is an example of a monosomy where the individual is born with only one sex chromosome, an X. Aneuploidy is a change in the number of chromosomes that can lead to a chromosomal disorder. ...


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 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 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: When a portion of one chromosome is transferred to another chromosome. There are two main types of translocations. In a reciprocal translocation, segments from two different chromosomes have been exchanged. In a Robertsonian translocation, an entire chromosome has attached to another at the centromere; these only occur with chromosomes 13, 14, 15, 21 and 22.
  • Inversions: A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted.
  • 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.

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. A genetic deletion is a genetic aberration in which part of a chromosome is missing. ... Wolf-Hirschhorn syndrome, also known as deletion 4p and 4p- syndrome was first described in 1961 by U. Wolf and K. Hirschhorn and their co-workers. ... Summary Jacobsen Syndrome, also known as 11q deletion, is a congenital disorder that occurs due to a partial deletion of the terminal band on chromosome 11. ... A duplication Chromosomal duplication occurs when a section of DNA is accidentally duplicated when a chromosome is copied. ... Chromosomal translocation of the 4th and 20th chromosome. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... An inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end. ... Formation of a ring chromosome. ...


Inheritance

Most chromosome abnormalities occur as an accident in the egg or sperm, and are therefore not inherited. Therefore, the abnormality is present in every cell of the body. Some abnormalities, however, can happen after conception, resulting in mosaicism (where some cells have the abnormality and some do not). Chromosome abnormalities 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 abnormality. Biological inheritance is the process by which an offspring cell or organism acquires or becomes predisposed to characteristics of its parent cell or organism. ... Mosaicism In medicine (genetics), a mosaic or mosaicism denotes the presence of two populations of cells with different genotypes in one patient, where usually one of the two is affected by a genetic disorder. ...


Reference

  • NHGRI. 2006. Chromosome Abnormalities

External links

  • MeSH Chromosome+disorders

  Results from FactBites:
 
ABNORMALITIES IN CHROMOSOME STRUCTURE (1824 words)
Abnormalities in chromosome structure follow a chromosome break and, during the repair process, the reunion of the wrong segments of the chromosome.
Individuals and families have been described with a translocation chromosome abnormality and a concurrent genetic condition; the genetic condition occurring because the chromosome breakpoint is in the midst of a gene.
In contradistinction, a numerical chromosome abnormality in a child is presumed to be due to a sporadic cell division error and parental chromosome studies are not indicated.
THE MERCK MANUAL, Sec. 19, Ch. 261, Congenital Anomalies (3704 words)
Chromosomes are the 46 rodlike structures seen during cell division in the nucleus of most human cells.
Chromosomes from single cells are usually photographed, their images cut out of the print and pasted onto a piece of paper, forming a karyotype.
The genitalia are frequently abnormal in both sexes; cryptorchidism and an abnormal scrotum occur in the male, and a bicornuate uterus occurs in the female.
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