Editing Needleman–Wunsch algorithm (section)

===Tracing arrows back to origin===
Mark a path from the cell on the bottom right back to the cell on the top left by following the direction of the arrows. From this path, the sequence is constructed by these rules:
* A diagonal arrow represents a match or mismatch, so the letter of the column and the letter of the row of the origin cell will align.
* A horizontal or vertical arrow represents an indel. Vertical arrows will align a gap ("-") to the letter of the row (the "side" sequence), horizontal arrows will align a gap to the letter of the column (the "top" sequence).
* If there are multiple arrows to choose from, they represent a branching of the alignments. If two or more branches all belong to paths from the bottom right to the top left cell, they are equally viable alignments. In this case, note the paths as separate alignment candidates.

Following these rules, the steps for one possible alignment candidate in figure 1 are:

 G → CG → GCG → -GCG → T-GCG → AT-GCG → CAT-GCG → '''GCAT-GCG'''
 A → CA → ACA → TACA → TTACA → ATTACA → -ATTACA → '''G-ATTACA'''
              ↓
     (branch) → TGCG → -TGCG → ...
              → TACA → TTACA → ...