Noncoding DNA in eukaryotes encodes functionally important signals for the regulation of chromosome assembly, DNA replication, and gene expression. The increasing availability of whole-genome sequences of related taxa has led to interest in the evolution of these signals, and the phylogenetic footprints they produce. Cis-regulatory sequences controlling gene expression are often conserved among related species, but are rarely conserved between distantly related taxa. Several experimentally characterized regulatory elements have failed to show sequence similarity even between closely related species.