Fitch's Algorithm

Tree Length Across Sites

A multi-site tree length is the sum of single-site parsimony scores.

highlighted = computed this step

Score each site on the same topology

For several sites, run the same Fitch score on the same tree. The chosen sites have scores 2, 0, and 1.

site scores=2,0,1\text{site scores}=2,0,1
Scores across sitesTree length is the sum of per-site parsimony scores.SiteScore122031total3

Tree length is the sum over sites

Adding the per-site scores gives tree length 3.

tree length=3\text{tree length}=3
Scores across sitesTree length is the sum of per-site parsimony scores.SiteScore122031total3