Final answer:
Telomeres, the protective caps at the ends of chromosomes, are the only physiological barrier to immortality encoded in DNA. Telomeres shorten each time a cell divides, eventually leading to cell senescence or programmed cell death.
Step-by-step explanation:
The only physiological barrier to immortality that is encoded in DNA is the shortening of telomeres.
Telomeres are the protective caps at the ends of chromosomes that help maintain their stability and integrity.
Each time a cell divides, telomeres become shorter, eventually reaching a critically short length that triggers cell senescence or programmed cell death.
This process is known as aging and is a natural biological mechanism that limits the lifespan of cells.