This fully-resourced lesson challenges the students to use fully labelled genetic diagrams to interpret the results of monohybrid and dihybrid crosses as detailed in topic 7.1 (Inheritance) of the AQA A-level Biology specification. Step-by-step guides are used to demonstrate how diagrams for the inheritance of one and two genes should be constructed and a focus is given to the areas where students commonly make mistakes, such as in writing out the gametes. The main task of each section of the lesson provides an opportunity for the students to apply their understanding by calculating phenotypic ratios. All of the questions have fully-explained mark schemes and students can assess their progress and address any misconceptions immediately. Key genetic terminology is used throughout the lesson and mirrors that used in actual exam questions.