The correct answer is c the mutant will show decreased levels of gene expression.
Explanation:
Histone acetyl transferase is an enzyme that helps in the transfer of acetyl group to the epsilon -NH2 group of lysine reside of histone proteins that surrounds the DNA molecule of chromosome.
This results to make the target DNA more assecible for transcription mediated by RNA polymerase resulting the gene expression.
On the other hand the mutant in which histones are not acetylated,transcription rate decreases as the non acetylated DNA is less assecible to RNA polymerase.
She should make observations next. If she doesnt make observations, it would be difficult to form a hypothesis and design an experiment, the result will more likely to be inaccurate too.