Sperm with XY chromosome must be caused by the first meiosis error. During the first meiosis, XY homologous chromosomes entered the same secondary spermatocyte, while the second meiosis proceeded normally, thus forming four abnormal sperm, two of which contained XY chromosomes and two did not contain sex chromosomes.

Sperm with YY chromosome must have made mistakes in the second meiosis. Under normal meiosis, during the second meiosis, the Y chromosome in the secondary spermatocyte with Y chromosome divides into the same spermatocyte because the two sister chromosomes do not divide into two daughter cells, thus forming a sperm without Y chromosome and another sperm with YY chromosome.