Which of the following disorders results from changes in an individual gene?

A. Turner syndrome

B. Klinefelter syndrome

C. Trisomy 21

D. Sickle-cell disease

The correct answer for the question that is being presented above is this one: "C. Trisomy 21." Trisomy 21 is a disorder results from changes in an individual gene. Down syndrome (DS or DNS), also known as trisomy 21, is a genetic disorder caused by the presence of all, or part of a third copy of chromosome 21.