How is down syndrome caused?

Down syndrome:

1. Down syndrome refers to a genetic disorder in which chromosome 21 has three copies due to abnormal cell division.
2. Generally, we have 23 chromosome pairs in each cell. One chromosome comes from the mother and the other one comes from the father.
3. During cell division, if chromosome 21 has an extra chromosome then down syndrome occurs.
4. If each cell has a part of an entirely extra chromosome 21 then translocation down syndrome occurs.
5. If an extra chromosome 21 is there in some cells then mosaic down syndrome occurs.