1. The problem statement, all variables and given/known data Hello, I am trying to understand the importance of proliferation limits and cell senescence. In particular, one of my homework questions is asking to compare the proliferation limit of Embryonic Stem cells (ES) and fibroblasts (which would be trans-differentiated) and describe how this difference plays a role when thinking about engineering organs, for example a heart transplant. 2. Relevant equations Hayflick limit for senescence is ~50 cell divisions. 3. The attempt at a solution Here is what I am thinking, however I am not sure if this is correct or not. Non-differentiated the ES cells can divide almost indefinitely, however when the stem cell differentiates into a specific function, it goes through approximately 50 cell divisions before senescence. On the other hand, fibroblasts have already gone through some cell divisions at the point when they are trans-differentiated. Therefore, their life before senescence is less than 50 cell divisions. Can someone verify this? How do ES cells and fibroblasts compare with regards to the Hayflick limit? Thank you.