B2.3.1

• In an early-stage embryo, the cells are unspecialised. They develop and become specialised for specific functions as the embryo grows.
• The development of cells in different ways to carry out specific functions is called differentiation.
• gene expression: every cell has every gene so they have all the information but they only use what they need and store everything else
• The position of a cell in the embryo determines how it differentiates. Gradients of signalling chemicals indicate a cells position in the embryo and determine which pathway of differentiation it follows.
• For example gradients of retinoic acid guide differentiation of cells in the development of forelimbs, pancreas, lungs, kidneys and other organs.