Patterns of chromosome evolution in ruminants.

Studying when and where gross genomic rearrangements occurred during evolution is key to understanding changes in genome structure with functional consequences that might eventually lead to speciation. Here we identified chromosome rearrangements in ruminants, a clade characterized by large chromosome differences. Using 26 genome assemblies, we reconstructed five ancestral karyotypes and classified the rearrangement events occurring in each lineage. With these reconstructions, we then identified evolutionary breakpoints regions (EBRs) and synteny fragments. Ruminant karyotype evolution is characterized by inversions, while interchromosomal rearrangements occurred preferentially in the oldest ancestor of ruminants. We found that EBRs are depleted of protein coding genes, including housekeeping genes. Similarly, EBRs are not enriched in high GC regions, suggesting that meiotic double strand breaks might not be their origin. Overall, our results characterize at fine detail the location of chromosome rearrangements in ruminant evolution and provide new insights into the formation of EBRs.