chromosome 21

Chromosome 21 is the smallest human chromosome and represents approximately 1.5% of the total DNA in cells.

Summary:Gene examples of chromosome 21:
  • autosome
  • small sized chromosome
  • about 46.900.000 base pairs
  • about 352 genes
 
OLIG2: This gene encodes a basic transcription factor which is produced in the brain. Transcription factors are proteins that bind to specific regions of DNA and help control the activity of particular genes. The gene is involved in a chromosomal translocation (rearrangements of genetic material between chromosomes) associated with acute lymphoblastic leukemia (lymphoid precursor cells (lymphoblasts) are arrested in an early stage of development and replace the normal elements of bone marrow, resulting in a marked decrease in the production of normal blood cells). The chromosomal location of OLIG2 is within a region of chromosome 21 which has been suggested

to play a role in learning deficits associated with Down syndrome (Down syndrome critical region).

The HLCS gene encodes the enzyme holocarboxylase synthetase. This enzyme attaches biotin, a B vitamin that is found in food, to other molecules. It is essential for the production and breakdown of proteins, fats and carbohydrates. Mutations in the HLCS gene can lead to holocarboxylase synthetase deficiency, that is an inherited disorder in which the body is unable to use the vitamin biotin effectively. If left untreated, these defects lead to serious medical problems like delayed development, seizures and coma.

chromosome overview (scaled down):
overview chromosome 21
Legend:
adenine (A)
thymine (T)
guanine (G)
cytosine (C)
not yet determined (N)
Legend:
adenine (A)
thymine (T)
guanine (G)
cytosine (C)
not yet determined (N)