For 10 points, name these repetitive sequences of DNA found at the ends of chromosomes.
In yeast, Rap1 and the Sir proteins congregate at these structures, which are located immediately next to the HML and HMR sites. Fluorescence  in situ  hybridization is combined with flow cytometry to analyze these structures. Most G-quadruplexes occur at them. An enzyme discovered in  Tetrahymena  and named for these structures is partly composed of a noncoding RNA that initiates reverse transcription. When cells (*)  over-express the enzyme named for these structures, they can surpass the Hayflick limit and become immortal. Because Okazaki fragments miss out on lagging strand sequence, these structures gradually shorten over adult lifetimes. For 10 points, name these repetitive sequences of DNA found at the ends of chromosomes.
In yeast, Rap1 and the Sir proteins congregate at these structures, which are located immediately next to the HML and HMR sites.
telomere s [or  telomerase ; prompt on  chromosome s] 