where D is the observed distance between gene sets i and j and d is the expected distance, computed as the sum of the lengths of the segments of the tree from gene set i to gene set j. The quantity n is the number of times each distance has been replicated. In simple cases n is taken to be one. If n is chosen more than 1, the distance is then assumed to be a mean of those replicates. The power P is what distinguished between the Fitch and Neighbor-Joining methods. For the Fitch-Margoliash method P is 2.0 and for Neighbor-Joining method it is 0.0. As running Fitch took a long time when the gene-set size was huge (weeks for the human gene-sets and months for the mouse gene-sets), Neighbor-Joining method was used to create the replicate dendrograms (not shown) after randomizing the input order for greater confidence. The resulting coefficient matrix files were displayed using the Phylodraw graphics program [18] .