Q. Your friend is studying mouse fur color and has isolated the GPCR responsible for determining its color, as well as an extracellular signal that activates the receptor. She finds that, on adding up the signal to pigment cells (cells that produce the pigment determining fur color), cAMP levels rise in the cell. She starts a biotech company, and the company isolates more components of the signaling pathway responsible for fur color. Using transgenic mouse technology, company genetically engineers mice that are defective in various proteins involved in determining fur color. The company obtains the follow results.

Normal mice have beige (very light brown) fur color.
Mice lacking the extracellular signal have white fur.
Mice lacking the GPCR have white fur.
Mice lacking cAMP phosphodiesterase have dark brown fur.

Your friend has also made mice that are defective in α subunit of the G protein in this signaling pathway. The defective α subunit works normally except that, once it binds GTP, it cannot hydrolyze GTP to GDP. What color do you guess that the fur of these mice will be? Why with reason?