Comparative analysis method employed. A three-step process identified gene structure variation. (a) D1 orthologs were identified in the other strains' genome sequences via best bidirectional BLASTn and syntenic conservation. (b) Orthologous sequences were then aligned (black lines) and the D1 gene structure was overlayed (red lines are exons, blue boxes are introns). (c) Introns were scanned for cases of precise intron excision relative to the reference strain D1.