Figure 1.

Position of the Boreoeutherian ancestor. Branch labels give the estimated number of chromosomal breaks from our study, also categorized as (interchromosomal, intrachromosomal). If conserved segments i and j are adjacent in the ancestral genome but not in the descendant genome, then we call the break interchromosomal if i and j are on different chromosomes in the descendant, and intrachromosomal otherwise. We suspect that many of the predicted intrachromosomal breaks in rat are assembly artifacts.