Question

klinefelters syndrome is a result of which of the following nondisjunction mutations?
three copies of the 21st chromosome
only an x chromosome
deletion of chromosome 5
two x chromosomes and a y

Explanation:

Klinefelter's syndrome is characterized by the presence of an extra X - chromosome in males, resulting in a karyotype of XXY. Three copies of the 21st chromosome cause Down syndrome, having only an X chromosome is Turner syndrome, and deletion of chromosome 5 causes Cri - du - chat syndrome.

Answer:

two X chromosomes and a Y