This engaging and fully-resourced lesson looks at the effects of stabilising, directional and disruptive selection as the three main types of selection. The PowerPoint and accompanying resources have been designed to cover point 17.2 (b) of the CIE International A-level Biology specification which states that students should be able to identify each type of selection by its effect on different phenotypes.
The lesson begins with an introduction to the mark, release, recapture method to calculate numbers of rabbits with different coloured fur in a particular habitat. This method is covered later in topic 18 so this section of the lesson is designed purely to generate changes in numbers of the organisms. Sketch graphs are then constructed to show the changes in the population size in this example. A quick quiz competition is used to engage the students whilst introducing the names of the three main types of selection before a class discussion point encourages the students to recognise which specific type of selection is represented by the rabbits. Key terminology including intermediate and extreme phenotypes and selection pressure are used to emphasise their importance during explanations. A change in the environment of the habitat and a change in the numbers of the rabbits introduces directional selection before students will be given time to discuss and to predict the shape of the sketch graph for disruptive selection. Students are challenged to apply their knowledge in the final task of the lesson by choosing the correct type of selection when presented with details of a population and answer related questions.