Cell specialization refers to the procedure, which takes place after cell differentiation where the newly produced cells are structurally converted so that they can do their activity efficiently and effectively.
One of the examples of specialized cells is red blood cells, which develops in bone marrow in many phases. From a hemocytoblast, a multipotent cell in the mesenchyme turns into an erythroblast; after two to five days of development, the erythroblast slowly gets occupied with hemoglobin, and its nucleus and mitochondria get disappear.
In the later phase, the cell is known as reticulocyte that eventually turns into a complete mature red cell. The average red cell in humans survives for 100 to 120 days.