Chromosome

:For information about chromosomes in genetic algorithms, see Chromosome (genetic algorithm).

Chromosomal aberrations

Some chromosome abnormalities do not cause disease in carriers, such as translocations, or chromosomal inversions, although it may lead to a higher chance of having a child with a chromosome disorder. Abnormal numbers of chromosomes or chromosome sets, Aneuploidy, may be lethal or give rise to genetic disorders. Genetic counseling is offered for families that may carry a chromosome rearrangement.

Related Topics:
Translocations - Chromosomal inversions - Aneuploidy - Genetic counseling

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The gain or loss of chromosome material can lead to a variety of genetic disorders. Examples include:

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• Cri du chat syndrome, which is caused by the deletion of part of the short arm of chromosome 5. The name cri du chat means cat's cry, this condition was called this because affected babies make high-pitched cries that sound like a cat. They have wide-set eyes, a small head and jaw and are moderately to severely mentally retarded and very short
• Wolf-Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4. It is characterized by severe growth retardation and severe to profound mental retardation.
• Down syndrome (extra chromosome 21). This is also known as mongolism or trisomy 21. Characteristics are decreased muscle tone, asymmetrical skull, slanting eyes and mild to moderate mental retardation.
• Edward's syndrome is the second most common trisomy after Down's Syndrome. It is a trisomy of chromosome 18. Symptoms include mental and motor retardation as well as numerous congenital anomalies causing serious health problems. 90% die in infancy, however those who live past their first birthday usually are quite healthy thereafter. They have a characteristic hand appearance with clenched hands and overlapping fingers.
• Patau Syndrome, also called D-Syndrome or trisomy-13. Symptoms somewhat similar to those of trisomy-18, but they don't have the characteristic hand shape.
• Jacobsen syndrome, also called the terminal 11q deletion disorder. A very rare disorder. More information at http://www.11q.org. They have normal IQ or mild mental retardation, with poor expressive language skills. Most have a bleeding disorder called Paris-Trousseau Syndrome.
• Klinefelter's syndrome (XXY). Men with Klinefelter syndrome are usually sterile. They tend to have longer arms and legs and tend to be taller than their peers. They are often shy, quiet boys, and have a higher incidence of speech delay and dyslexia. During puberty, some of them grow breasts and get a curvy figure.
• Turner syndrome (X instead of XX or XY). In Turner syndrome, female sexual characteristics are present but underdeveloped. People with Turner syndrome often have a short stature, low hairline, abnormal eye features and bone development and a "caved-in" appearance to the chest.
• XYY syndrome. XYY boys are usually taller than their brothers. They are more likely to be hyperactive, enjoying active games. Despite what was previously belived, XYY boys are no more likely than other boys to be violent.
• Triple-X syndrome (XXX). XXX girls tend to be tall and thin and are often shy. They have a higher incidence of dyslexia.
• small supernumerary marker chromosome. This means there is an extra, abnormal chromosome. Features depend on the origin of the extra genetic material. Cat-Eye Syndrome and Isodicentric chromosome 15 syndrome are both caused by a supernumerary marker chromosome, as is Pallister Killian Syndrome.

You can find a detailed graphical display of all human chromosomes and the diseases annotated at the correct spot at http://www.ornl.gov/hgmis/posters/chromosome/.

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