Down Syndrome Is Also Known as Trisomy-21 Because Individuals with Down

Multiple Choice

Down syndrome is also known as trisomy-21 because individuals with Down syndrome ____.

A) have three distinct facial features by the 21st week of pregnancy
B) show three distinct temperament patterns by the 21st week of infancy
C) have a third chromosome on the 21st pair
D) have 21 genes on the 3rd pair of chromosomes