Balanced chromosomal rearrangements could lead to unbalanced segregation gametes during meiosis. In this Study, sperm flourescence ill situ hybridization (FISH) analysis of meiotic segregation products of four reciprocal translocations; 46,XY,t(7;10)(q21;q22), 46:XY,t(15;17)(q11;p12), 46,XY, t(6;13)(p21.1;q32), and 46,XY,t(1;13)(q24;q10) are presented. In three Out Of these four cases with t(15;17), t(6;13), and t(1;13) additional blastomere FISH analyses are also provided. multi-color FISH analysis was applied using diverse probe combinations specific for translocated chromosome segments. The average frequency of sperm nuclei bearing unbalanced products for t(7;10), t(15:17), t(6;13), and t(1;13) were 48.7%, 59.5%, 60.5%, and 62.9%, respectively. Frequencies of blastomeres comprising unbalanced products in Cases with t(15;17), t(6;13), and t(1:13) were 80% (12 of 15), 60% (3 of 5), and 50% (2 of 4), respectively. Chi-square test analysis showed significant differences in the meiotic segregation pattens Clue to the distribution and numbers of the chiasmatas that Could depend oil the size of the translocated segments (P < 0.001). In conclusion, FISH analysis of sperm and blastomere for reciprocal translocation carriers effectively estimates the approximate risk Of unbalanced products and this result might ensure Valuable genetic Counseling. (c) 2006 Wiley-Liss, Inc.