Your friend works in a lab that is studying why a particular mutant strain of Drosophila grows an ...

Your friend works in a lab that is studying why a particular mutant strain of Drosophila grows an eye on its wing. Your friend discovers that this mutant strain of Drosophila is expressing a transcription factor incorrectly.
 
  In the mutant Drosophila, this transcription factor, which is normally expressed in the primordial eye tissue, is now misexpressed in the primordial wing tissue, thus turning on transcription of the set of genes required to produce an eye in the wing primordial tissue. If this hypothesis is true, which of the following types of genetic change would most likely lead to this situation?
  (a) a mutation within the transcription factor gene that leads to a premature stop codon after the third amino acid
  (b) a mutation within the transcription factor gene that leads to a substitution of a positively charged amino acid for a negatively charged amino acid
  (c) a mutation within an upstream enhancer of the gene
  (d) a mutation in the TATA box of the gene