Down syndrome, or Down's syndrome (primarily in the United Kingdom, trisomy 21, is a chromosomal condition caused by the presence of all or part of an extra 21st chromosome. It is named after,Joh who described the syndrome in 1866. The condition was identified as a chromosome 21 trisomy by Jeromd in 1959. Down syndrome in a fetus can be identified with amniocentesis during pregnancy, or in a baby at birth.
Down syndrome is a chromosomal condition characterized by the presence of an extra copy of genetic material on the 21st chromosomeither in whole ( trisomi21) or part (such as due to translocations). The effects and extent of the extra copy vary greatly among people, depending on genetic history, and pure chance.
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