Totipotent cells are unique types of stem cells that have the ability to develop into any cell type in an organism, including both the embryonic and extra-embryonic tissues. This means they can form all the different cell types needed for a complete organism, such as muscle cells, nerve cells, and blood cells. Totipotency is most commonly observed in the earliest stages of development, specifically in the fertilized egg, or zygote. As development progresses, cells begin to specialize and lose their totipotent capabilities. After a few divisions, the cells become pluripotent, meaning they can still form many cell types but not all, particularly the extra-embryonic tissues. Understanding totipotency is crucial in fields like regenerative medicine and developmental biology, as it provides insights into how organisms grow and develop from a single cell.