Active conservation of noncoding sequences revealed by three-way species comparisons

Human and mouse genomic sequence comparisons are being increasingly used to search for evolutionarily conserved gene regulatory elements. Large-scale human-mouse DNA comparison studies have discovered numerous conserved nonco ding sequences of which only a fraction has been functionally investigated A question therefore remains as to whether most of these noncoding sequence s are conserved because of functional constraints or are the result of a la ck of divergence time.