Downs Syndrome also called Trisonomy 21, occurs when the 21st chromosome has a third chromosome instead of the usual 2 or pair.
a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
Humans have 46 chromosome pairs
There are 3 different ways that Downs Syndrome can occur depending upon how the cells divide when first conceived:
- – Trisonomy 21 (95% of cases_ All cells of the body have the extra chromosome
- – Translocation (4-5% of cases) An extra copy of chromosome 21 is attached to another chromosome.
- – Mosaicism (less than 1% of cases) some cells have the usual 46chromosomes but others have the extra 21st