Dear all, I just found this great place to discuss science! I was wondering if anyone has an idea that roughly how many Drosophila genes have a phenotype when mutated? I think I have read it somewhere that only 1/3 of the genes would give a phenotype but am not entirely sure about that. Could anyone please help me out? Thank you

That question is somewhat meaningless without context. Even point mutations that are not neutral (i.e. the altered genetic code yields the same amino acid, but even then there are certain exceptions) will at the very least result in an altered phenotype on the biochemical (i.e. protein) level. The effects increase with the amount of changes (a knockout will have stronger effects, for example).

 

Whether these has any further effects depends on how and at which resolution you look at the organism. For example, if your criterion is survival, under certain environmental conditions a complete deletion may be harmless (e.g. if it disrupts some synthesis reactions, but you feed the fly the nutrient externally it may not matter), but looking at it on the biochemical level, the disruption would be fairly obvious.