It is relatively new discovery. We now understand that DNA strands are usually tightly wrapped around histones. This resembles strings wrapped around beads. Ge

It is relatively new discovery. We now understand that DNA strands are usually tightly wrapped around histones. This resembles strings wrapped around beads. Gene expression is talking about the myriad number of things that causes the DNA strands to relax and unwound from the histone. By exposing that piece of DNA strand the gene can be expressed and the resulting protein is formed. I don’t believe we have a complete understanding yet of what causes genes to be expressed or not expressed. There seem to be multiple factors at play. My understanding of telomeres is that is primarily a mechanism to prevent cancer. After a cell replicates itself a number of times the telomeres grow shorter and shorter and at a certain point it stops replicating because the assumption is the DNA has now been damaged by environmental factors. Some cells don’t have this mechanism and can replicate infinitely eg skin cells.