Final answer:
In a typical somatic mammalian cell, about 70-80% of CpGs are typically methylated, affecting gene expression and playing a role in conditions like cancer.
Step-by-step explanation:
In a typical somatic mammalian cell, a significant portion of CpGs are methylated. DNA methylation occurs within CpG islands, which are stretches high in cytosine and guanine dinucleotides. These regions are found in promoter regions of genes and are subject to methylation, where a methyl group is added to the cytosine residue. Methylated genes are usually silenced or their expression is regulated in some way. Methylation can silence genes during development and can be influenced by dietary or environmental conditions. In terms of percentage, while it can vary among different cell types and organisms, a common estimate is that around 70-80% of CpGs in mammalian somatic cells are methylated. This methylation can be an important factor in regulating gene expression and is also a significant aspect in diseases such as cancer, where hypermethylation leads to gene silencing.