________ is an inherited disorder caused by an extra 21st chromosome that results in intellectual disability.

Question

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Down syndrome is caused by an extra, third copy of chromosome 21, resulting in intellectual disability and other physical characteristics. Phenylketonuria is a genetic disorder, but it is caused by a mutation in a single gene rather than an entire chromosome. Huntington's disease is caused by a mutation in the HTT gene, also not related to chromosome 21. Turner's syndrome is caused by a missing or incomplete second sex chromosome, not an extra chromosome 21.

________ Is an Inherited Disorder Caused by an Extra 21st