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Name: Ong
Status: Student
Grade:  Other
Location: N/A
Country: Singapore
Date: June 2006

Hi, I am a female 10 year student from Singapore.I stumbled into your site and how wonderful it is to be able to ask any questions on science.I was wondering what happens if a person has more or less chromosomes.

With the exception of Turner's syndrome (females with only one X xhromosome), there are no known examples of humans with less than 46 chromosomes. Presumably when an embryo lacks a chromsome, it is lethal. The most common example of humans having an extra chromosome is Down's syndrome which is caused by an extra chromosome #21. This results in sever mental retardation and many physical abnormalities. Extra or missing chromosomes are rare because they almost always result in death of the embryo. This is demonstrated by the fact that when spontaneously aborted fetuses are examined, a high incidence of chromosome abnormalities is observed in such fetuses.

Ron Baker, Ph.D.

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