Biology Question #564

Cynthia Everhart, a 31 year old female from Leesburg asks on January 18, 2002,

My neice is being tested for an unknown cause to her developemental delay. She has recently been tested for Fragile X syndrome. I know that Down syndrome is a 23 chromasome syndrome. My question is: what is the 21 chromasome syndrome called? I saw it on the discovery channel once but can't remeber what it was called. I seem to recall that is was something like Missing E. I'm not sure.

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The answer

Barry Shell answered on January 18, 2002

We all have a 23 chromosomes that occur in pairs to make a total of 46. Down Syndrome happens when an individual gets 3 #21 chromosomes, instead of two. That is called "Trisomy". This can happen with other chromosomes, like 18, 9, 13, to name a few, but I found no obvious reference of trisomy with chromosome #23. Maybe you are thinking of "polyploidy", the condition of having 3 sets of chromosomes instead of two.

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