Question 3
(Multiple Choice)
A researcher notices that women working in the petrochemical industry who are exposed to aromatic hydrocarbons may have a greater incidence of breast cancer than women without such exposure. The researcher undertakes a study of the BRCA1 promoter using the restriction enzymes MspI and HpaII. MspI cleaves double-stranded DNA at 5'-CCGG-3' regardless of whether the CG in the middle has cytosine methylation, whereas HpaII cleaves double-stranded DNA at 5'-CCGG-3' only when the CG in the middle lacks cytosine methylation. For a region of double-stranded DNA in the promoter region of BRCA1, tumor cells from the breasts of exposed women with breast cancer and nontumor cells from breasts from the same women show the illustrated patterns of bands produced by MspI and HpaII: 
Which of the following statements are supported by this evidence?
A)More sites are methylated in tumor cells than in nontumor cells.
B)Fewer sites are methylated in tumor cells than in nontumor cells.
C)The same sites are methylated in tumor cells as in nontumor cells.
D)No sites are methylated in nontumor cells.
E)The BRCA1 gene may be epigenetically silenced in tumor cells.
Answer
A, E