Similar screens are more difficult to carry out in other multicellular organisms, including mammals (as a model for humans), due to technical reasons, and their results are less clear. However, various methods have been developed for the nematode worm C. elegans,[41] the fruit fly,[42] and zebrafish[43] (see table). A recent study of 900 mouse genes concluded that 42% of them were essential although the selected genes were not representative.[44]