The diagram shows a section of the karyotype from a human donor. Chromosome pairs 19 through 22 are labeled.

The diagram shows human chromosomes numbers 19, 20, 21, and 22. Three #23 chromosomes are present. Numbers 19, 20, and 22 show a pair each.

Which statement describes the gametes that joined together to form this karyotype?
A. The gametes formed normally, and then one chromosome was added when they joined together.
B. The gametes formed normally, and then one chromosome split apart when they joined together.
C. One gamete formed abnormally because a pair of homologous chromosomes failed to separate.
D. Both gametes formed abnormally because in each gamete, one pair of homologous chromosomes failed to separate.