The single reference design. 1A shows an example of a pairwise distance matrix for the tree below the matrix. In 1B the distances of other taxa to W, typical of a single reference design. Below it is the star topology constructed from these distances when no other information is available to differentiate distances among X, Y, and Z.
Gilbert et al. BMC Genomics 2011 12:456 doi:10.1186/1471-2164-12-456