Sevenless (sev) is a gene in the fruit fly Drosophila melanogaster that encodes a receptor tyrosine kinase protein essential to the development of the R7 photoreceptor cells in the Drosophila embryonic eye.
[1] The Drosophila ommatidium contains 8 distinct retinula or R cells, each of which has a different spectral sensitivity.
The R7 photo receptor, located in each of several ommatidia in the fly's compound eye, is used to detect ultraviolet light.
[2] The R8 photoreceptor contains an activator of the RTK (receptor tyrosine kinase) for on a precursor R7 cell, called the bride of sevenless (BOSS).
The binding of BOSS to sevenless stimulates a complex series of reactions involving the RTK (sevenless), MAP kinases, Ras and many more molecules to differentiate that precursor R7 photo receptor to a fully functional R7 photo receptor that can see UV light.