Genome building blocks and block boundaries of the ancestral karyotype mapped onto B. rapa chromosome A3. The position of AK genome building blocks in chromosome A3 was defined by a comparison of B. rapa-A. thaliana syntenic relationships and the A. thaliana-AK mapping results [20, 29]. AK segments are labeled and oriented by arrows. Putative orthologs delineating the boundaries of recombination events are designated. CDs between AK blocks are indicated by dotted arrows. CEN, centromere.