Every organism comes from a single Cell

Development refers to the process by which cells divide, specialize and organize in time and space, into organs and tissue, making the organism. An important constraint is preserving germline.

Developmental processes

• Proliferation –Cell division
• Cell specialization
• Interaction – Cell signalling
• Cell movement – Morphogenesis

Cell proliferation, specialization, itnteraction, movement. Achieved by a Gene expression cascade in space!

Model organisms

From GEB

_{There are two major distinct problems here. One is that of cellular differentiation: how do different cells, sharing exactly the same DNA, perform different roles- such as a kidney cell, a bone marrow cell, and a brain cell? The other is that of morphogenesis ("birth of form"): how does intercellular communication on a local level give rise to large-scale, global structures and organizations- such as the various organs of the body, the shape of the face, the suborgans of the brain, and so on? Although both cellular differentiation and rnorphogenesis are poorly understood at present. the trick appears to reside in exquisitely fine-tuned feedback and "feedforward" mechanisms within cells and between cells, which tell a cell when to "turn on" and when to "turn off" production of various proteins.}