How does a fertilized 1-cell egg become a complex organism with billions of different cells (like us)? human body as drawn by Leonardo Da vinci Recipe to make an animal from a fertilized egg: 1. Make more cells (cell division) 2. Make many KINDS of cells starting from 1 cell (differentiate nerve cell, blood cell, skin cell, hair cell, muscle cell etc.) 3. Make the cells form tissues and organs at the right time and place (morphogenesis, organogenesis) 4. Make the various tissues and organs connect and function together in synergy to make a living animal ! How do we study these questions? We use “Model Organisms” such as the worm, C. elegans or the common aquarium fish, zebrafish. Why do we use “model organisms”? Because they are simple, grow fast in laboratory conditions, and are easy to manipulate and observe. Its easy to do experiments with them (especially if they don’t talk back to you !) What kinds of experiments can you do with these animals? You can study the functions of genes: genetics and genomics You can observe cells and tissues form as they happen in real time in a living animal, especially if parts are “labeled” with a visible marker, which emits light of a certain wavelength: cell & developmental biology You can manipulate them in various ways: treat with specific substances (chemicals or mutagens): chemical genetics You can physically manipulate them and see the outcome: mechanobiology You can see how cells or tissues grow back after injury: Stem cells & regeneration Human egg cell (not to scale)