(a) Phylogenetic network of mir-1 sequences. Despite the short sequences, the major clades are well separated in this phylogenetic network: there are two vertebrate groups, mir-1-1 and mir-I-2, both of which show a tetrapod and a teleost branch; arthropoda and nematoda are also clearly separated; only the basal deuterostomes do not fit very well due to their diverged sequences. (b) Phylogenetic network of mir-30 sequences, which occur in three clusters each consisting of two miRNAs genes (see inset). A tandem duplication of the ancestral mir-30 sequence gave rise to a single cluster which was duplicated subsequently. Not all details of the duplication history can be resolved due to the short sequence length. It is clear, however, that the duplication events pre-dated the last common ancestor of tetrapoda and teleosts. It is plausible to associate these cluster duplications with the genome duplications at the origin of the vertebrate lineage. Networks were reconstructed using the neighbor net method.