In the human body we have chromosomes which contain our DNA. In development, the human cell has 46 chromosomes.
Those chromosomes come in two sets: the first set of 23 chromosomes comes from the individual’s mother in the form of the egg, and the second set of 23 chromosomes comes from the individual’s father in the form of the sperm.
The chromosome pairs are numbered 1 through 23. The first 22 chromosome pairs are called autosomes. The 23rd pair is called the sex chromosomes. These are the chromosomes referred to as X and Y.
The type of sex chromosomes an individual has determines the gender. For example, women have two XX chromosomes, while men have one X chromosome and one Y chromosome.
When there is a chromosomal abnormality, something has occurred that has disrupted the number of chromosomes or the structure of the chromosomes.
In cases of a numerical chromosomal abnormality, the individual does not have the normal 23 pairs of chromosomes. Instead, she may be missing one of the chromosomes from a pair or has more than two chromosomes in one pair.
If a chromosome is missing, it is called a monosomy. If there are more than two chromosomes, it is called a trisomy.
An example of a trisomy is Down syndrome, which is also called Trisomy 21, as the individual has three chromosomes in pair 21.
Symptoms of Down syndrome include small hands and feet, poor muscle tone, and a flat face. Several health conditions can occur with Down syndrome, including thyroid problems, hearing problems and dementia, according to the National Institute of Child Health and Human Development.
Turner syndrome is an example of a monosomy. With this numerical chromosomal abnormality, the individual is female, but only has one X chromosome.
Individuals with this disorder have small jaws, extra folds of skin around their neck, and are short in stature. Individuals with this disorder do not have prominent female secondary sexual characteristics, according to Palomar College.
The other group of chromosomal abnormalities are structural chromosomal abnormalities, in which the structure of the chromosome becomes affected.
Four types of structural abnormalities may occur. These are rings, inversions, deletions, translocations and duplications.
With rings, part of the chromosome breaks off and curves into a ring. The National Human Genome Research Institute noted that in these cases, genetic material may be lost or it may not.
With inversions, part of the chromosome also breaks off, but it reattaches after turning upside down.
In cases of deletion, a part of the chromosome is deleted, with that genetic material lost.
If a translocation occurs, part of one chromosome moves to another chromosome.
The last type of structural abnormality, duplications, involves the gaining of extra genetic material, as part of the chromosome is duplicated.
References
National Human Genome Research Institute. Chromosomes. Web. 9 May 2012
http://www.genome.gov/26524120
National Institute of Child Health and Human Development. Down Syndrome. Web. 9 May 2012
http://www.nichd.nih.gov/health/topics/down_syndrome.cfm
Palomar College. Sex Chromosome Abnormalities. Web. 9 May 2012
http://anthro.palomar.edu/abnormal/abnormal_5.htm
Genetics Home Reference. Are Chromosomal Disorders Inherited?. Web. 9 May 2012
http://ghr.nlm.nih.gov/handbook/inheritance/chromosomalinheritance
National Human Genome Research Institute. Chromosome Abnormalities. Web. 9 May 2012
http://www.genome.gov/11508982
Reviewed May 9, 2012
by Michele Blacksberg RN
Edited by Jody Smith