Evolution of the Caenorhabditis elegans Genome
this should partially explain the high insertion rate in worm: http://mbe.oxfordjournals.org/content/26/6/1199.full
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Of the new mutations observed in MA lines, more than half were short indel mutations, with fewer deletions than insertions (Denver, Morris, Lynch, and Thomas 2004). This finding on indels contrasts with previous work with C. elegans pseudogenes in which deletions are more common than insertions (Robertson 2000; Witherspoon and Robertson 2003) but is consistent with findings in C. elegansmicrosatellite mutation data (Frisse 1999; Denver, Morris, Kewalramani, et al. 2004; Seyfert et al. 2008).
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