Final answer:
Tandemly repetitive DNA consists of sequences found in centromeres and telomeres of eukaryotic chromosomes, protecting coding sequences from degradation. Telomeres have the repetitive sequence TTAGGG, and their maintenance is aided by telomerase. Therefore, the correct answer is that tandemly repetitive DNA makes up centromeres and telomeres.
Step-by-step explanation:
Tandemly repetitive DNA is a type of sequence that makes up a significant portion of eukaryotic genomes. Specifically, it constitutes the structures known as centromeres and telomeres. Telomeres are the ends of linear chromosomes and consist of noncoding repetitive sequences that protect coding sequences from degradation during cell division. In humans, this sequence is TTAGGG repeated hundreds to thousands of times. The discovery of the enzyme telomerase was crucial in understanding how these chromosome ends are maintained. Unlike telomeres, tandemly repetitive DNA is not generally associated with euchromatin, which contains actively transcribed genes. Nor does tandemly repetitive DNA typically encode proteins. The repetitive DNA can sometimes be spread through the movement of transposable elements, but this is not their primary cause. Based on this information, the correct answer to the student's question is that tandemly repetitive DNA is what makes up centromeres and telomeres.