Chromosome 21
Chromosome 21
Chromosome 21 (pronounced /ˈkroʊməˌsoʊm/ twenty-one) is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 21 spans about 48 million base pairs (the building material of DNA) and represents approximately 1.5 percent of the total DNA in cells.
Etymology
The term "chromosome" comes from the Greek words for color (chroma) and body (soma). Scientists gave this name to chromosomes because they are cell structures, or bodies, that are strongly stained by some colorful dyes used in research.
Related Terms
- Down Syndrome: A condition in which a person has an extra copy of chromosome 21. This extra copy changes the body's and brain's normal development and causes mental and physical challenges for the person.
- Alzheimer's disease: Early-onset Alzheimer's disease is often associated with Chromosome 21. This is because the gene that produces the amyloid precursor protein, associated with Alzheimer's disease, is located on Chromosome 21.
- Leukemia: Acute lymphoblastic leukemia is associated with a translocation between chromosomes 12 and 21.
- Hirschsprung disease: A disease associated with mutations in a gene on chromosome 21. It affects the large intestine of newborns, babies, and children, causing problems with passing stool.
See Also
External links
- Medical encyclopedia article on Chromosome 21
- Wikipedia's article - Chromosome 21
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