Stem cells are the only totipotent cells in humans. The fertilization of an egg gives rise to a stem cell that is undifferentiated and can form any part of the human body. This cell divides and creates more totipotent stem cells for the first four days of embryonic development.
Totipotent stem cells are the most versatile cells in the human body. One totipotent stem cell is capable of producing a placenta and any type of human body tissue. Totipotent stem cells can be extracted from an embryo and allowed to divide in a controlled culture, making them useful in genetic engineering, gene therapy, and transplants.
Once the first four days of embryonic development are over, stem cell division produces cells that are considered pluripotent. Pluripotent cells are able to develop into any kind of tissue needed by the fetus, but can't develop into the tissue needed for the placenta. From these pluripotent stem cells, multipotent stem cells develop. Multipotent stem cells are more specialized, giving rise to a range of cells within a tissue type.
Adult stem cells are able to repair or replace dead cells within a specific tissue. They can only operate within a specific tissue range and are considered multipotent stem cells.