As a result of _______, male XX and female XY are occasionally seen

Sometimes the transfer of X and Y chromosomal segments results in male XX and female XY. 

A twofold break in the chromosomes accompanied by the union of the surviving pieces results in a deletion, which is the loss of an intercalary region of a chromosome. 

Aneuploidy refers to the presence of more or fewer chromosomes than the typical number for the species' DNA.