The karyotype for trisomy 21 illustrates an example of a genetic mutation caused by a) insertion. b) inversion. c) crossing over. d) nondisjunction.

Trisomy 21, as illustrated by the karyotype, is caused by nondisjunction. This occurs when chromosomes do not separate properly during meiosis.

Answer is D) nondisjunction

The correct answer is option C, that is, nondisjunction.

Explanation:

Trisomy 21, also called Down syndrome is a result of the error in the cell division known as nondisjunction. It leaves an egg or sperm cell with an additional copy of chromosome 21 prior to or after conception.  

The phenomenon of nondisjunction can take place during anaphase of meiosis or mitosis. At the time of anaphase, the homologous chromosomes or the sister chromatids get separate and move to the contrary poles of the cell, with the help of microtubules. However, in nondisjunction, this separation does not take place.