Down's Syndrome or Trisomy 21 is a genetic condition affecting an individual's mental and physical abilities. It is the most common chromosomal condition associated with retardation and is caused by an error during cell development. Down's Syndrome occurs amongst all ethnic groups. The condition can usually be diagnosed during pregnancy or at birth.
Down's Syndrome was first recognised in 1866 by English doctor, John Langdon Down. He described the condition and it was later given his name. The cause of the condition was unknown until 1959 when Professor Jerome Lejeune proved that Down's Syndrome was a chromosomal irregularity. Lejeune noted the presence of an extra chromosome 21 and it was later discovered that additional chromosomal material was the associated with developmental abnormalities.
People with Down's Syndrome have 47 chromosomes instead of the usual 46 chromosomes. The cause is the presence of an extra copy of chromosome 21. This can occur as a whole extra chromosome or as extra parts of the chromosome (translocation).
Boy with Down Syndrome using cordless drill to ass...
Stendhal Syndrome
Serotonin SyndromeThe seriousness of the condition depends largely on the extent of the extra copy. That is, an individual who only has a small amount of additional chromosome material will not be affected as severely as an individual with a full copy of chromosome 21. The image below shows the extra copy of chromosome 21.
Chromosome 21 is duplicated because of a random event or 'mistake' in cell development. This chromosome comes from either the mother, father or during pregnancy. During cell division, a parent may produce an abnormal cell with 24 chromosomes instead of 23. If this cell is fertilised, the baby will have 47 chromosomes instead of 46. Since cells continue to copy genetic information, the extra chromosome is duplicated throughout the baby's cells. The child born will have Down's Syndrome.
The extra chromosome can also...