Final answer:
CpG islands are regions with a high frequency of cytosine and guanine pairs in the promoter regions of genes. Methylation of these cytosines can lead to gene silencing, but not all CpG islands are always methylated, nor are they exclusively associated with imprinted genes. CpG islands can occur in various genes and typically also contain enhancers and promoters. The answer is option D.
Step-by-step explanation:
The CpG islands are regions within DNA that contain a high frequency of CG dinucleotide pairs and are often found in the promoter regions of genes. The methylation of cytosine bases in CpG islands can lead to gene silencing, because this epigenetic modification can change how the DNA interacts with regulatory proteins and histones, resulting in a tightly coiled and transcriptionally inactive state.
However, the statement that the C bases in CpG Islands are always methylated is false, as methylation patterns can vary, and not all CpG islands are methylated in all cells or at all times. Additionally, the claim that genes with CpG Islands do not have enhancers or promoters is incorrect; these regulatory elements are typical features of eukaryotic genes. Also, the statement that only imprinted genes have CpG Islands is inaccurate, as CpG islands can be found in various genes, not solely those that are imprinted. Methylation of the C bases in a CpG Island can indeed silence the promoter of the gene, contributing to the regulation of gene expression and playing a critical role in disease processes such as cancer.