Prab at 17:46, 9 October 2020

2020-10-09T17:46:35Z

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Chromosome abnormalities, as the name suggests, are genetic disorders affecting the [[chromosome]].
[[File:Single Chromosome Mutations.png|alt=Single Chromosome Mutations|thumb|Single Chromosome Mutations]]
== Types ==
There are different types of chromosome abnormalities: Numerical or structural.

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== Numerical chromosome abnormalities ==
A numerical abnormality mean an individual is either missing one of the chromosomes from a pair or has more than two chromosomes instead of a pair.
[[File:Numerical chromosome aberration.png|alt=Numerical chromosome aberration|thumb|'''Numerical chromosome aberration''']]
An example of a condition caused by numerical abnormalities is Down syndrome, which is marked by mental retardation, learning difficulties, a characteristic facial appearance and poor muscle tone (hypotonia) in infancy. An individual with Down syndrome has three copies of chromosome 21 rather than two; for that reason, the condition is also known as Trisomy 21. An example of monosomy, in which an individual lacks a chromosome, is Turner syndrome. In Turner syndrome, a female is born with only one sex chromosome, an X, and is usually shorter than average and unable to have children, among other difficulties.
[[File:Human chromosome diseases set en.png|alt=Human chromosome diseases set|thumb|Human chromosome diseases set]]
== Structural abnormality ==
A structural abnormality means the chromosome's structure has been altered in one of several ways.

* Structural Abnormalities: A chromosome's structure can be altered in several ways.
** Deletions: A portion of the chromosome is missing or deleted.
** Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material.
** Translocations: A portion of one chromosome is transferred to another chromosome. There are two main types of translocation. 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.
** Inversions: A portion of the chromosome has broken off, turned upside down, and reattached. As a result, 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.
[[File:Schematic illustration of chromosomal aberrations.svg|alt=Schematic illustration of chromosomal aberrations|thumb|Schematic illustration of chromosomal aberrations]]
== How does it happen? ==
Most chromosome abnormalities occur as an accident in the egg or sperm. In these cases, the abnormality is present in every cell of the body. Some abnormalities, however, happen after conception; then some cells have the abnormality and some do not.

== Inheritance ==
Chromosome abnormalities can be inherited from a parent (such as a translocation) or be "''de novo''" (new to the individual). This is why, when a child is found to have an abnormality, chromosome studies are often performed on the parents.

== How do chromosome abnormalities happen? ==
Chromosome abnormalities usually occur when there is an error in cell division. There are two kinds of cell division, mitosis and meiosis.
[[File:Screening and counseling for genetic conditions - a report on the ethical, social, and legal implications of genetic screening, counseling, and education programs (IA screeningcounsel00unit).pdf|alt=Screening and counseling for genetic conditions|thumb|Screening and counseling for genetic conditions]]
* Mitosis results in two cells that are duplicates of the original cell. One cell with 46 chromosomes divides and becomes two cells with 46 chromosomes each. This kind of cell division occurs throughout the body, except in the reproductive organs. This is the way most of the cells that make up our body are made and replaced.
* Meiosis results in cells with half the number of chromosomes, 23, instead of the normal 46. This is the type of cell division that occurs in the reproductive organs, resulting in the eggs and sperm.

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In both processes, the correct number of chromosomes is supposed to end up in the resulting cells. However, errors in cell division can result in cells with too few or too many copies of a chromosome. Errors can also occur when the chromosomes are being duplicated.

Other factors that can increase the risk of chromosome abnormalities are:

* Maternal Age: Women are born with all the eggs they will ever have. Some researchers believe that errors can crop up in the eggs' genetic material as they age. Older women are at higher risk of giving birth to babies with chromosome abnormalities than younger women. Because men produce new sperm throughout their lives, paternal age does not increase risk of chromosome abnormalities.
* Environment: Although there is no conclusive evidence that specific environmental factors cause chromosome abnormalities, it is still possible that the environment may play a role in the occurrence of genetic errors.
== See also ==
* [[Aneuploidy]]
* [[Chromosome segregation]]
* [[Genetic disorder]]
** [[List of genetic disorders]]
* [[Gene therapy]]
* [[Nondisjunction]]
* [[Obstetrical complications]]

==External links==
* {{MeshName|Chromosome+disorders}}

{{Chromosomal abnormalities}}
{{Mutation}}

{{Authority control}}

[[Category:Chromosomal abnormalities]]
[[Category:Cytogenetics]]
[[Category:Genetics concepts]]

Chromosome abnormality - Revision history

Prab at 17:46, 9 October 2020