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Inherited Disorders

Chromosome Abnormalities And Disease

Some inherited diseases are attributed to damaged or improperly distributed chromosomes and are termed chromosomal diseases. Chromosomes are long strands of DNA complexed with proteins and RNA that condense and allow for equal distribution of the genes when cells divide. Each chromosome contains hundreds or thousands of genes, and every cell needs to have two copies of each chromosome in order to maintain genetic balance. At the time of conception, an extra copy or missing copy of a chromosome or even a part of a chromosome disrupts normal development. Most chromosomal abnormalities result from simple accidents of chromosome segregation and, as such, they tend not to recur in families. One example of genetic disorder that results from chromosomal imbalance is Down syndrome. This condition is caused by the presence of an extra copy of chromosome 21.



Jorde, L.B., J.C. Carey, M.J. Bamshad, and R.L. White. Medical Genetics. 2nd ed. St. Louis: Mosby-Year Book, Inc., 2000.

Thompson, M.W., R.R. McInnes, and H.F. Willard. Thompson & Thompson Genetics in Medicine. Philadelphia: W. B. Saunders Company, 1996.

Robert G. Best


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Autosome or autosomal chromosome

—Chromosomes other than sex chromosomes. In humans, all chromosomes except the X and Y sex chromosomes.


—Long strands of DNA complexed with proteins, which contain the genetic information. At the time of conception, an extra, missing, or damaged copy of a chromosome or even a part of a chromosome disrupts normal development.

Sex chromosomes

—In humans the X and Y chromosomes are termed sex chromosomes. Normal males carry one X and one Y chromosome, normal females carry two X chromosomes in their somatic cells. Somatic cells are all cells other than sex or germ cells (e.g., spermatozoa or ova).

Additional topics

Science EncyclopediaScience & Philosophy: Incomplete dominance to IntuitionismInherited Disorders - Chromosome abnormalities and disease