Answer:
a) The mutation affects a transcription factor that binds to HOX3A gene sequences.
Explanation:
The mutation can affect a transciption factor that promotes HOX3A transcription. For example, if the mutation causes the transcription factor not to be synthesized, there will be no signal required to initiate HOX3A transcription. On the other hand, if the mutation generates changes in the form of the transcription factor, it may not be recognized in the promoter region of the HOX3A gene.