Physical maps of the F, W and X1 mitotypes. The schematic shows the arrangement of introns (thick lines) within the polymorphic region of the U. maydis LSU rRNA gene (drawn to scale). The three major exon sequences are boxed and numbered from I to III. Stippled lines connect homologous exon sequences. Intron regions amplified by the primer combinations ‘a’ (W type specific) and ‘b’ (F type specific) are marked in grey. The schematic is adapted from  with permission granted by the Genetics Society of America.