Hi, Shawn. Down syndrome (DS) or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. Down syndrome is the most common chromosome abnormality in humans. It is typically associated with a delay in cognitive ability (mental retardation, or MR) and physical growth, and a particular set of facial characteristics. The average IQ of young adults with Down syndrome is around 50, whereas young adults without the condition typically have an IQ of 100. (MR has historically been defined as an IQ below 70.) A large proportion of individuals with Down syndrome have a severe degree of intellectual disability. For more info, here's the site that has more information:
It is when a person is born with an extra chromosome. It affects the way the person thinks and develops. My cousin has down syndrome. She is the sweetest person I have ever met, and she does not let her difference affect who she is.
Down Syndrome is a genetic mutation where there are three copies made of the 21st chromosome. Thus, the person exhibiting this mutation will have 47 chromosomes instead of the normal number of 46, 23 coming from each parent.