In
developmental biology,
cellular differentiation is the process of a
cell changing from one
cell type to another. Most commonly this is a less specialized type becoming a more specialized type, such as during
cell growth. Differentiation occurs numerous times during the development of a
multicellular organism as it changes from a simple
zygote to a complex system of
tissues and cell types. Differentiation continues in adulthood as
adult stem cells divide and create fully differentiated
daughter cells during tissue repair and during normal cell turnover. Some differentiation occurs in response to
antigen exposure. Differentiation dramatically changes a cell's size, shape,
membrane potential,
metabolic activity, and responsiveness to signals. These changes are largely due to highly controlled modifications in
gene expression and are the study of
epigenetics. With a few exceptions, cellular differentiation almost never involves a change in the
DNA sequence itself. Thus, different cells can have very different physical characteristics despite having the same
genome.