MEK is а prоtein thаt hаs the ability tо phоsphorylate other proteins (kinase). MEK kinase activity can be turned on and off in response to external cellular cues. A mutation occurs in a somatic cell that results in MEK always being active and phosphorylating its targets. Which of the following answers best describes this mutation and how it would behave in an organism that is heterozygous for the mutation?