If all the cells in our body have the same DNA, then why aren't they all the same kind of cell? How can there be different cell types, shapes, and functions?
Because each has a different subset of the whole genome turned on. Some functions are common to all cells - they will have active genes for say tubulin and spectrin, as all will have a cytoskeleton of some ilk for example - so all cells will have those genes 'turned on', though the levels of activity will differ depending on cell type. Other genes are specific to a given cell type - you only get haemoglobin in red blood cells.There is are further layer of controls over how much of a given gene product is made, all cells have tubulin, but some types will have more than others, and these regulators themselves are under genetic control.And the action of all these gene products together detrmine the form and function of the cell. And cells do chnage their gene expression over time as they are newly formed, mature and die. The way skin cells work, dividing in deeper layers and accumulating keratin as they are pushed towards the outside of the organism and eventually becoming dead slabs of keratin and flaking off is one example.An explanation with a video -What Is Cell Differentiation? - Process, Importance & Examples - Video & Lesson Transcript | Study.com These might help, but Wiki articles can be a bit impenetrable at times -Regulation of gene expression Cellular differentiation Trying to work out these processes is a major field of research as getting a fully differentiated cell back down a few steps or even all the way being a stem cell would be a very handy thing to do.http://www.wellcome.ac.uk/About-...