A new type of Robertsonian translocation (1/26) in a bull with unilateral cryptorchidism, probably occurring de novo.

The karyotype of a Holstein-Friesian bull with unilateral cryptorchidism was investigated according to the G-, C- and Cd-banding techniques. By G-banded karyotyping, it was shown that this bull had 1/26 Robertsonian translocation. Furthermore, there were 2 dark dots at the centromere of 1/26 translocated chromosome by C- and Cd-banded karyotyping. Although the chromosomes of the parents of this bull were not examined, 12 half-sib cows from different sires or dams did not show any chromosomal aberrations. The semen quality of the father and the conception rate of the parents were within the normal range in Japan. From the results obtained, it appears that this translocation resulted from a centric fusion at the early embryonic stage and had occurred de novo.