Final answer:
Mitotic divisions occur in the stratum basale and stratum spinosum layers of the epidermis, where stem cells divide to form new cells and continue to grow before moving upwards and ceasing division.
Step-by-step explanation:
The layers of the epidermis where mitotic divisions occur are the stratum basale (also known as stratum germinativum) and the stratum spinosum. The stratum basale is the deepest layer of the epidermis and contains stem cells which divide to form new cells. Above this layer is the stratum spinosum, where the newly formed cells continue to divide. However, as keratinocytes move away from these mitotic layers and into higher levels, such as the stratum granulosum and the stratum corneum, they stop dividing and start to die and become part of the protective barrier of the skin.