We have examined 389 father/son sample pairs from U.S. Caucasians, African Americans, Hispanics and Asians using the 17 Y-STR loci in the Yfilertrade mark kit and observed a total of 24 differences between father and son. Thirteen mutations resulted in the gain of a repeat in the son and 11 resulted in a loss of a repeat. All samples resulted in single repeat mutations except one sample which contained a two repeat loss at Y-GATA-H4. Furthermore, two different sample pairs were found to have two mutations. An African American sample pair had a mutation at DYS458 and a second at DYS635 and an Asian sample pair had mutations at DYS439 and Y-GATA-H4.