Scheme of Work Cambridge International as & a level

Extension activity: Learners carry out further research to consider occasions in which a gene is ‘switched on’ or ‘off’ in response to stimuli. Examples include developmental genes including those that determine gender, stem cell characteristics and growth.

Past and specimen papers

Past/specimen papers and mark schemes are available to download at www.cambridgeinternational.org/support (F)

17: Selection and evolution

Syllabus ref. and Key Concepts (KC)	Learning outcomes	Suggested teaching activities
17.1 Variation KC3	17.1.1 Explain, with examples, that phenotypic variation is due to genetic factors or environmental factors or a combination of genetic and environmental factors. 17.1.2 Explain what is meant by discontinuous variation and continuous variation. 17.1.3 Explain the genetic basis of discontinuous variation and continuous variation. 17.1.4 Use the t-test to compare the means of two different samples.	Learners list as many features as they can that we can use to recognise each other. Examples may include hair and eye colour, height, weight, age, sex, and so on. Ask learners to also list features that cannot be seen – such as ABO blood group and tidal volume. Identify which are examples of continuous variation, and which are examples of discontinuous variation. Elicit the idea that genetic and environmental factors tend to be unequal in their contribution to traits that illustrate discontinuous variation and continuous variation. Developing on the previous activity, learners collect data from classmates. Learners then use the t-test to compare means of, for example, height or hair length between males and females, for example. A useful website to support analysis using the t-test is: www.theseashore.org.uk/theseashore/Stats%20for%20twits/T%20Test.html Prepare learners for the next lesson (on natural and artificial selection) by providing a series of questions for them to research in advance using internet sources. Questions may include ‘What is the importance of variation between members of a species?’ and ‘What are the benefits of producing sexually rather than asexually?’ (I)
17.2 Natural and artificial selection