Scheme of Work Cambridge International as & a level

Extension activity: Learners suggest why the Hardy–Weinberg equations cannot be used if there are multiple alleles, or if there is a codominant relationship between the alleles, and how selection, the founder effect and genetic drift, including the bottleneck effect, invalidate the equations.

17.3 Evolution KC3 KC4 KC5	17.3.1 Outline the theory of evolution as a process leading to the formation of new species from pre-existing species over time, as a result of changes to gene pools from generation to generation. 17.3.2 Discuss how DNA sequence data can show evolutionary relationships between species. 17.3.3 Explain how speciation may occur as a result of genetic isolation by: geographical separation (allopatric speciation) ecological and behavioural separation (sympatric speciation).	Show the Tree of Life, which is a short animated video showing how the process of evolution is thought to have occurred: www.youtube.com/watch?v=H6IrUUDboZo. Inspired by this, learners work in pairs to construct a one-sentence definition for the term ‘evolution’. They submit their work in the form of sticky notes to the board, or on a shared electronic document or word cloud (Multimeter). Highlight key terms that are common to many learners’ submissions (expected: ‘change,’ ‘selection’ and ‘extinction’); and examples (some learners may write ‘Darwin’s finches’, ‘peppered moth’, and ‘antibiotic resistance’). Learners suggest the traditional types of evidence used to investigate relatedness between different organisms (e.g. comparative morphology and anatomy, fossils, classification and embryology). Provide learners with the DNA sequences of a section of a gene common to four or five different species (e.g. cytochrome-c oxidase). Challenge learners to suggest how this can be used to show evolutionary relationships between the species. Useful animation to describe speciation: http://nortonbooks.com/college/biology/animations/ch17a01.htm Other resources on evolution: https://evolution.berkeley.edu/evolibrary/resourcelibrary.php Provide learners with a number of past paper questions related to evolution, and they work in pairs to construct the questions. Discuss the suggestions learners have submitted. (F)