Figure 1. The difference between positional homology alignment and glocal alignment.

Three example linear genomes are broken into genes labeled A,B,C,D, and R. R is a multi-copy (repetitive) gene, with different copies labeled using numeric subscripts. Each copy of R is assumed to be identical in sequence, so that orthology/paralogy is unknowable from nucleotide substitution (as is often the case with mobile DNA repeat elements). Genes shifted downward in a given genome are inverted (reverse complement) relative to the reference genome. The positional homology alignment would ideally create two local alignment blocks where each block has exactly one alignment row for each genome. Only positionally-conserved copies of the repetitive gene family R become aligned to each other. The glocal alignment would ideally create four local alignment blocks wherein all copies of the repetitive gene family become aligned to each other.