Question

All of your cells (except rbcs and platelets) have the same genotype, so why are they different?

Answer 1

All of our cells originate from diploid zygote. So genetic complement of all the cells are same. Although we have different cells in our body with different function and structure. This is due to the reason that in different cells different sets of genes are active and other genes remain inactive.

For example, In liver cells (hepatocytes) the genes which produce enzymes required for digestion or other liver specific function remain active and expressed while the genes responsible for visibility or light perception remain inactive. On the other hand, in the cells present in our retina of eye, such as rod and cone cells, the genes required for light perception remain active whereas genes for digestion of foods remain inactive. Although in all kinds of cells of our body, the genes which are required for cell maintenance and basic metbolism always remain turned on and express constitutively such as genes for glycolysis or TCA cycle.

So, we can understand due to this differential gene expression in specific type of cells the different cells of our body function differently according to their need.