Final answer:
Stretches of DNA with a high number of CpG sites near gene promoters are called CpG islands. These regions impact gene expression through methylation and are distinct from telomeres, introns, and exons, which have other genetic functions.
Step-by-step explanation:
Stretches of DNA of 1000-2000 bp in length containing a high number of CpG sites and found near gene promoters are called CpG islands. These regions have a high frequency of cytosine and guanine dinucleotide DNA pairs (CG) and are often located in the promoter regions of genes. The cytosines in these CpG sites can be methylated, altering how the DNA interacts with regulatory proteins and histones, thus affecting gene expression.
Telomeres are the protective ends of linear chromosomes consisting of noncoding repetitive sequences. They prevent coding sequences from degradation due to cell division. Introns and exons are parts of eukaryotic genes where introns are non-translated intervening sequences and exons are the translated sequences that determine the amino acid sequence of polypeptides. Unlike CpG islands, telomeres, introns, and exons play different roles in genetic structure and regulation.