The purpose of this tutorial is to let you experience with two methods that are often used by molecular biologists: 1. Screening DNA libraries for new genes 2. Amplifying genes by PCR . We present here an experimental problem. You will try to solve it by performing various virtual experiments. Each experiment will be followed by several multiple choice questions. The different answers will lead you to additional comments and explanations. Wrong answers can lead you to valuable comments and insights, so don't rush through the tutorial.