Genetic screens for enhancers and suppressors of temperature-sensitive loss-of-function mutations in sevenless (sev) in Drosophila melanogaster led to the discovery of some other genes involved in the Ras-MAP-kinase pathway. Would you expect loss-of-function mutations in genes encoding each of the following proteins to be an enhancer (E) or suppressor (S) of sev? An enhancer mutation exacerbates the effect of the original mutation, whereas a suppressor mutation alleviates it. Note that loss-of-function mutations can be just partial defects and not necessarily null mutations. Your answer would be a four-letter string composed of letters E and S only, e.g. EEEE.
( ) Sos
( ) Ras
( ) Ras-GAP
( ) Raf

Question

Genetic screens for enhancers and suppressors of temperature-sensitive loss-of-function mutations in sevenless (sev) in Drosophila melanogaster led to the discovery of some other genes involved in the Ras-MAP-kinase pathway. Would you expect loss-of-function mutations in genes encoding each of the following proteins to be an enhancer (E) or suppressor (S) of sev? An enhancer mutation exacerbates the effect of the original mutation, whereas a suppressor mutation alleviates it. Note that loss-of-function mutations can be just partial defects and not necessarily null mutations. Your answer would be a four-letter string composed of letters E and S only, e.g. EEEE.
( )	Sos
( )	Ras
( )	Ras-GAP
( )	Raf

Quizplus · Accepted Answer

Activation of Sevenless signaling leads to the activation of Sos, Ras, and Raf proteins. Consistently, loss-of-function mutations in genes encoding these proteins would exacerbate the effect of sev loss-of-function mutations. Defects in Ras-GAP, however, would suppress the effect.

Genetic Screens for Enhancers and Suppressors of Temperature-Sensitive Loss-Of-Function Mutations