In 1998 Rosbach, Hall and colleagues discovered the cycle gene, clock gene, and cryptochrome photoreceptor in Drosophila through the use of forward genetics, by first identifying the phenotype of a mutant and then determining the genetics behind the mutation. 
Order of authorship in the original publication: Rutila, Suri, Le, So, Rosbash, Hall. Digital text from cell.com at this link.

See also: Stanewsky, R.; Kaneko, M.; Emery, P.; Beretta, B.; Wager-Smith, K.; Kay, S.A.; Rosash, M.; Hall, J. C.,  "The cry^b Mutation Identifies Cryptochrome as a Circadian Photoreceptor in Drosophila," Cell, 95, 1998, 681-682.