QUESTION 152 (6 marks)
The matrix shows differences in a conserved DNA region from five hypothetical species. E is a known outgroup. Assume the stated distances reliably reflect relatedness. A and D have similar feeding structures; their common ancestor lacked those structures.
| Species | A | B | C | D | E |
|---|---|---|---|---|---|
| A | – | 1 | 4 | 4 | 8 |
| B | 1 | – | 4 | 4 | 8 |
| C | 4 | 4 | – | 1 | 8 |
| D | 4 | 4 | 1 | – | 8 |
| E | 8 | 8 | 8 | 8 | – |
a) Identify both closest pairs and cite their distances. [2 marks]
b) Draw a rooted cladogram consistent with the matrix and outgroup. [2 marks]
c) Explain why the feeding-structure similarity does not outweigh the molecular evidence that A and D are not sister species. [2 marks]
Practice marking scheme
Answer
A–B and C–D are sister pairs. Rooted topology: (((A,B),(C,D)),E). The similar feeding structures in A and D can be explained by convergent evolution and do not make them the closest pair.
Working
A–B and C–D each differ by one unit, while every comparison between the two pairs differs by four. E is more distant from all four and roots the tree. Similar environmental demands can favour independently acquired feeding structures in lineages that are not sisters; shared derived molecular patterns provide evidence distinct from that functional similarity.
Marking criteria
- Identifies A and B with distance 1. [1 mark]
- Identifies C and D with distance 1. [1 mark]
- Draws the two sister pairs joining within one ingroup. [1 mark]
- Roots E outside that ingroup. [1 mark]
- Identifies possible convergent evolution/independent acquisition from an ancestor lacking the feature. [1 mark]
- Explains that similar selection/function can produce similar morphology without closest ancestry. [1 mark]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusCompare your working with the guide above.