Editing Developmental Biology (section)

== 2. Cellular Differentiation ==

Because nearly every cell in an organism contains the exact same DNA genome, how do cells become so remarkably different in structure and function? The answer is cellular differentiation—the process by which a less specialized cell becomes a more specialized cell type.

=== Potency ===
A cell's ability to differentiate into different types is called its potency.
* '''Totipotent:''' Can differentiate into any embryonic or extra-embryonic cell type (e.g., the zygote and early cleavage cells).
* '''Pluripotent:''' Can differentiate into any of the three germ layers, but not extra-embryonic tissues like the placenta (e.g., embryonic stem cells).
* '''Multipotent:''' Can differentiate into a restricted range of closely related cell types (e.g., hematopoietic stem cells in the bone marrow can become various types of blood cells, but not neurons).

=== Gene Regulation ===
Differentiation is driven by the strict regulation of gene expression. As a cell progresses down a developmental pathway, specific transcription factors and epigenetic modifications (like DNA methylation) permanently silence genes that are no longer needed while activating cell-specific genes. The cell does not lose DNA; it simply changes which chapters of the instruction manual it reads.