Mongolism Underlying Cause
Normally, a person has 23 pairs of chromosomes. One of each pair is donated from the mother, and one from the father. Down's syndrome occurs when there is an extra 21st chromosome. The extra chromosome can come from the mother's egg or the father's sperm. However, in most cases, it comes from the mother's egg. It is unknown why the egg or sperm carries the extra chromosome. The syndrome results from the directions that the cells receive from this extra DNA.
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