Fig. 4. MicroRNA family conservation. MicroRNAs can be grouped into families according to primary sequence similarity. As a cut-off, we used less than five conserved nucleotides out of the first eight. This Venn diagram shows the conservation of microRNA families between C. elegans, D. melanogaster and mammals. Primary sequence data was obtained from MiRBase version 7.0 (Griffiths-Jones, 2004).