Y chromosome length variation and its significance in the horse.

The results of Y chromosome measurements in 31 horses are presented. The Y chromosome was identified using G-, R-, and C-banding techniques. From G-banded metaphase spreads, total X and Y chromosome and separate proximal (P) and distal (D) Y-band measurements were made. Within this group, the Y/X ratio (%) for each animal varied from 18.93 to 43.95, with an overall mean of 34.85 and a coefficient of variation (CV) of 16.12. The overall mean P/X ratio (%) was 23.57 with a CV of 20.57, compared with an overall mean D/X ratio (%) of 11.26 with a CV of 15.18. The group studied included 27 Thoroughbred and 4-non-Thoroughbred animals, of which 20 were clinically normal controls and 11 presented with various clinical abnormalities. By comparison with data from other species, the possible breed association and clinical significance of the observed heteromorphism for the Y chromosome in this species is discussed.