Which of the Following Statements Concerning Down Syndrome Is FALSE

Multiple Choice

Which of the following statements concerning Down syndrome is FALSE?

A) Down syndrome is also referred to as Trisomy 21.
B) In Down syndrome, there is a defective gene on the X chromosome.
C) Down syndrome is the single most common genetic cause of mental retardation.
D) In Down syndrome, babies are born with an extra 21st chromosome.