• Quick retrieval from earlier learning (Evidence for evolution and how new species form; Classification levels and scientific (binomial) names). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Approximate % difference between human DNA and other primates: chimpanzee 1.2 %, rhesus macaque 7 %, orangutan 3.1 %. Which primate shares the most recent common ancestor with humans? (chimpanzee / orangutan / rhesus macaque) → chimpanzeePrompt: Fewer DNA differences means less time since the two lines split.
2. Approximate % difference between human DNA and other primates: orangutan 3.1 %, chimpanzee 1.2 %, gorilla 1.6 %. Which primate shares the most recent common ancestor with humans? (gorilla / chimpanzee / orangutan) → chimpanzeePrompt: Fewer DNA differences means less time since the two lines split.
3. Approximate % difference between human DNA and other primates: rhesus macaque 7 %, gorilla 1.6 %, orangutan 3.1 %. Which primate shares the most recent common ancestor with humans? (orangutan / gorilla / rhesus macaque) → gorillaPrompt: Fewer DNA differences means less time since the two lines split.

• Show a microscope image of cells and ask what students think they are looking at.
• Share the objective: Read cladograms and shared derived traits. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: A cladogram branches in this order: lamprey, shark, frog, lizard, mouse. New traits: jaws appears before the shark branch; four limbs appears before the frog branch; amniotic egg appears before the lizard branch; hair appears before the mouse branch. Does the shark have four limbs?
• Step 1: four limbs appears after the shark branches off, so it lacks it.
• Step 2: So the answer is: no
• Answer: no
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. A cladogram branches in this order: lamprey, shark, frog, lizard, mouse. New traits: jaws appears before the shark branch; four limbs appears before the frog branch; amniotic egg appears before the lizard branch; hair appears before the mouse branch. Does the frog have hair? (yes / no) → noPrompt: A trait is shared by every branch that splits off after it appears.
2. A cladogram branches in this order (first branch = most distantly related): moss, fern, pine, sunflower. Which of these options is most closely related to the pine? (moss / fern / sunflower) → sunflowerPrompt: Organisms that branch off later are more closely related to each other.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 6 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. A cladogram branches in this order: lamprey, shark, frog, lizard, mouse. New traits: jaws appears before the shark branch; four limbs appears before the frog branch; amniotic egg appears before the lizard branch; hair appears before the mouse branch. Does the shark have amniotic egg? (yes / no) → noPrompt: A trait is shared by every branch that splits off after it appears.
2. On a cladogram, what does each node (branch point) represent? (a common ancestor / a species alive today / a fossil site / an extinction) → a common ancestorPrompt: Two lines meet where their lineages split.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-12.