Figure 1

A rooted binary tree with two most parsimonious labelings of internal nodes. a) The B functions of the Fitch algorithm calculated in the bottom-up phase. b) The (canonical) Fitch solution. c) The values calculated in the Sankoff-Rousseau algorithm and the edges in the metagraph M (see text for details). For readability, only those values are indicated that contribute in estimating the number of most parsimonious solutions. Also, vertices of the tree are not indicated, i.e. s(k) is written instead of s(v, k). From positioning, it should be obvious which s value belongs to which vertex. d) The most parsimonious solution that can be obtained only by the Sankoff-Rousseau algorithm and not by the Fitch algorithm.