Final answer:
d. Methylation is the epigenetic modification to DNA that affects gene expression without changing the DNA sequence. It involves the addition of a methyl group to the DNA molecule within specific regions called CpG islands. This modification can be influenced by environmental factors and can be heritable.
Step-by-step explanation:
d. Methylation is the epigenetic modification to DNA that affects gene expression without changing the DNA sequence. Methylation involves the addition of a methyl group to the DNA molecule, specifically within specific regions called CpG islands.
Methylation of genes usually leads to gene silencing, although it can have other regulatory effects as well. This modification can be influenced by environmental factors and can be heritable through cell division.