Reconstruction of the ancestral karyotypic lineages of the S. cerevisiae portion of the S. pastorianus genome. By examining the karyotypes of the two strains that share the furthest divergence point within Group 1, and assuming that S. cerevisiae DNA sequences can only be lost, not gained de novo, each S. cerevisiae chromosome of the putative shared ancestor can be reconstructed as the merging of all S. cerevisiae segments present in both strains, using the iterative process described in Methods. This figure shows the reconstructed ancestors for the two subgroups within the Group 1 S. pastorianus strains on the left, and the final reconstructed ancestor for the entire Group 1 on the right. Applying this logic to Group 2, the reconstructed ancestor for Group 2 is an organism with a complete S. cerevisiae genome (data not shown).
