A gene in Drosophila melanogaster that controls the development of R7, the seventh photoreceptor cell within an ommatidium (q.v.). In the absence of the wild-type allele of sevenless, R7 develops as a cone cell. It appears that the protein encoded by this cell fate gene is a membrane-bound receptor that transmits positional information that controls the type of differention the R7 cell undergoes. See Chronology, 1986, Tomlinson and Ready; developmental control genes, ommatidium, selector genes.
Subjects: Genetics and Genomics.