In Which of the Following Double-Mutant Flies Will R7 Photoreceptors

Question

In which of the following double-mutant flies will R7 photoreceptors develop normally?
A)constitutively active Raf and inactive MAPK
B)constitutively active MAPK and inactive Ras
C)constitutively active Ras and inactive Raf
D)all of the above
E)none of the above

Accepted Answer

R7 photoreceptor development requires the MAPK signaling pathway to be active. In choice B, having constitutively active MAPK ensures that the pathway is active even if Ras is inactive, allowing for normal R7 development. Other options disrupt the pathway upstream of MAPK, preventing its activation.