How many genes does D. melanogaster have?
EDIT

Personal correspondence to representative at FlyBase.org


  In FlyBase we have been gathering information about genes and phenotypes for over 20 years including information from papers and resources older than that.  We annotate gene models on the Drosophila melanogaster genome assembly and when possible associate those annotations with other information (eg. phenotype, function etc) that is known about the gene.  However, in some cases, especially for genes and phenotypes that were described in the older literature before the genome was sequenced we still have some information about those genes but have been unable to associate that information with a genome annotation.   Those are what we call unlocalized genes (i.e. those without a annotation on the genome).