A gene X is expressed in brain and leg region in an organism. The gene has two switches: one that activates it in the brain (let's call it brain switch) and another that activates it in the leg (let's call it leg switch). Each is activated by a different activator protein; lets call them brain switch activator and leg switch activator. A mutation (accidental change in DNA sequence) leads to an individual of the species being born with X expression only in the brain. Where might the mutation have occurred?
a) in the promotor of gene X
b) In the leg switch sequence OR in the gene sequence coding for leg switch activator
c) In the gene X
d) Only in the leg switch sequence