IB DP Biology- A3.2 Classification and cladistics- IB Style Questions For HL Paper 2 -FA 2025
▶️ Answer/Explanation
(a)
• Root: The root is the base of the cladogram and represents the oldest ancestral lineage from which all groups in the diagram have evolved.
• Node: A node is a branching point where one ancestral line splits into two. It marks the most recent shared ancestor of the organisms that branch off from that point.
(b)
Protein amino acid sequences provide a molecular basis for determining evolutionary relatedness. They are useful because:
• Mutations in DNA lead to changes in the amino acid sequence of proteins.
• These changes accumulate gradually, allowing scientists to estimate how long ago species diverged.
• Species with similar amino acid sequences are interpreted as being more closely related than those with many differences.
Because molecular data are less subjective than physical traits—which may evolve independently due to similar environments—the method is considered highly reliable for constructing cladograms.
(c)
Acceptable examples include:
• DNA base sequences
• rRNA gene sequences
• Shared morphological features (homologous structures)
• Karyotype comparisons (chromosome number and structure)
(d)
Parsimony analysis applies the principle that the simplest explanation is most likely correct. When several cladograms fit the data, the preferred one is the cladogram that requires the fewest evolutionary changes (e.g., minimum number of mutations or trait shifts). This minimizes unnecessary assumptions about how species evolved.