Year 10 Science · Unit 1 · Lesson 15
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Learning Goals
Read the graph
Illustrative selected-sequence similarity (%)
Classroom graph-reading values only, not measured percentages of whole-genome identity. Actual similarity depends on the sequences and comparison method used.
(a) Describe the overall trend shown in the graph.
(b) Using the illustrative graph values, calculate the difference between the chimpanzee and mouse comparisons in percentage points.
(c) Explain how greater similarity in comparable DNA sequences can support closer evolutionary relatedness. Why can this illustrative graph alone not establish actual divergence dates?
Real-world context
Australia separated from the supercontinent Gondwana approximately 50 million years ago, drifting northward in complete isolation. During this time, marsupials diversified to fill every ecological niche. Today, Australia has a sugar glider (a marsupial) that looks and behaves almost identically to the North American flying squirrel (a placental mammal). DNA analysis confirms they are not closely related, the sugar glider is more closely related to kangaroos than to any squirrel.
(a) Explain what convergent evolution is, and use the sugar glider and flying squirrel as your example.
(b) What does the independent evolution of similar forms in Australia and elsewhere tell us about the power of natural selection?
1. What is a molecular clock and what assumption does it rely on?
2. Why might students find it surprising that humans and bananas share some homologous genes? Explain what this gene-level evidence suggests about common ancestry, and why it should not be described as a percentage of whole-genome DNA similarity.
Wrap Up
In one sentence, what was the main idea of this lesson?