Figure 4

Centromere tandem repeat monomers are conserved only between closely related species. (a) Percentage identity between candidate centromere repeat sequences plotted against estimated divergence time. We averaged percentage identity between comparisons to generate a single value for each node in the phylogenetic tree (Figure 2). To accommodate unresolved relationships, we repeated the analysis on random resolutions of the tree. One such analysis is shown (quantitative results were very similar between analyses). (b) For primates and grasses, the phylogenetic signal was tested using Blomberg's K analysis for three different parameters: repeat monomer length, repeat monomer GC content and genomic abundance. In primates both repeat length and GC content were more conserved than expected (K > 1), whereas genomic abundance was less conserved than expected by a model of Brownian evolution (K < 1). Though K < 1 for all three traits in the grasses, none were significantly different from 1. P-values are shown in brackets.