Identification of Cryptic Evolutionary Rearrangements Between Cattle (Bovinae) and Goat (Caprinae) X Chromosomes

Cattle (Bos taurus, BTA) and goat (Capra hircus, CHI) are members of the Bovidae family, whose divergence into the Bovinae and Caprinae subfamilies occurred approximately 20 million years ago. These two species sharing the same diploid number (2n = 60) and having entirely acrocentric autosomes; moreover, they display remarkable chromosomal conservation, with only two known autosomal differences: a small translocation between BTA9 and CHI14, and an inversion on chromosome 13. Conversely, sex chromosome evolution in Bovidae is considerably faster, as reflected in the morphological and structural differences between the X chromosomes of cattle (submetacentric) and goat (acrocentric). Previous studies identified three large conserved regions between BTAX and CHIX, showing near-perfect conservation between the distal region of BTAXq and the proximal region of CHIX. In the present study, we aimed to detect potential small-scale evolutionary rearrangements that may have been overlooked by standard cytogenetic methods. Using fluorescence in situ hybridization (FISH), we identified an inversion of approximately 3 Mb between the cattle and goat X chromosomes. Additionally, our analysis revealed two assembly errors within the goat genome. These findings refine the current understanding of Bovidae sex chromosome evolution and emphasize the importance of high-resolution cytogenetic approaches.