Figure 1.

The equivalence between the SPR distance and MAF size. (a) The species tree S and gene tree G differ only in the placement of the gray subtree. The roots of these trees are denoted by ρ. (b) The MAF of S and G is produced by cutting the dotted edge in both trees. (c) Each component of an MAF other than the component containing ρ represents an SPR move. A single SPR move transforms S into G by moving the gray subtree in S to its position in G. (d) Each SPR move models an LGT event in the reverse direction. From the MAF of S and G we infer that a transfer of gene G has occurred from an ancestor of taxon 1 to an ancestor of taxon 4.