= Solution
\b[An activating <Ras> lesion is a parsimonious candidate], because <Ras> lies upstream of the branch to <Raf> and the branch to <phosphoinositide 3-kinase>. Persistent <GTP>-bound <Ras> can therefore produce both basal patterns through a single change. A lesion restricted to <MEK> would not directly explain the simultaneous <Akt> signal. The blot does not uniquely locate the mutation: a constitutively active upstream <receptor tyrosine kinase> or altered regulation of <Ras> could also activate both branches. Test the <Ras> nucleotide state, sequence relevant <genes>, and determine which targeted perturbation suppresses both outputs.
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