Converting one character into another character using the cyclic group. (a) depicts the cyclic group Σ
, which consists of the identity and the three substitution types for nucleotide character states. (b) In order to convert the character GTAGA into ACCTC using this group, we need to introduce the operation . As the operation s′also transforms the constant character AAAAA to CGCGC, converting GTAGA into ACCTC is equivalent to evolving the character state A at the root along the tree such that the character CGCGC is attained at the leaves. The Fitch algorithm applied to the latter produces a unique most parsimonious solution of three substitutions as depicted by (c).