Kostika Sofroni, via facebook asked:
I know that bones are formed from cartilage tissue. Then how is possible that in the human body we can also find cartilage tissue undifferentiated in bones?
We put this to Professor Tim Skerry...
Tim - Well this is a question that goes to even more fundamental biology than about the skeleton particularly, because it’s really the issue which is called patterning – how cells in your fingertip know they're fingertip cells, different from liver cells, different from eye cells. Cartilage cells which are cartilage that's going to become bone have some sort of positional information in their set of genetic information which tells them what to do. Whereas cartilage cells that are going to be at the surface of a joint have a different set of information. So, it’s a patterning issue rather than just – they're not – all cartilage cells aren’t the same.
Chris - There's a set of instructions written into them that tell them what to become basically.
Tim - Yes and knowledge about where they are.