How does having an extra chromosome effect the cell in Down's syndrome?!

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Answers:
The difficult answer is that nobody really knows for sure at this point. Somehow having three versions of the genes in chromosome 21 results in the changes associated with Down's Syndrome. Many researchers are studying the effects of individual genes, but those are only parts of the whole. For a more detailed look, search for "trisomy 21" in

http://www.pubmed.org

Other Answers:
It sends the wrong genetic information into the living cells, henceforth you have a down syndrome child with various degrees of abnormalities.
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