With each round of DNA replication, the chromosome will develop more and more errors in the genetic code, making continued rounds of DNA replication impossible.

Every cell is genetically programmed to have a certain lifespan. When this lifespan expires the cell undergoes apoptosis

Chromosomal DNA in some organisms have a preset limit on the number of DNA replications it can endure

Immune cells are responsible for marking each cell as they divide. When the immune cells recognise that a particular cell reaches the re-determined limit of cellular divisions, the cell is marked for destruction by apoptosis