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← Theoretical A

Q3 — Bacterial Phylogenomics (RNA Polymerase vs Transposase)

Theoretical A Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Molecular Systematics

Yerzhan studies the evolution of four closely related bacterial strains (A, B, C, D), focusing on RNA polymerase subunit β and transposase. He reconstructed phylogenetic trees for the two corresponding genes that code for these proteins (Figure 1X, Y) using the alignment of four sequences (representative snapshot is shown on Figure 2) and the most parsimonious solution. He rooted both phylogenies using the D strain as an outgroup. Unfortunately, he realized that he forgot to properly label the datasets. Consequently, he began comparing these phylogenetic trees to the reference phylogenetic tree reconstructed from genes of ribosomal proteins (Figure 1Z).

    X          Y          Z
   ┌─ C       ┌─ A       ┌─ A
 ┌─┤         ┌─┤         ┌─┤
 │ └─ B      │ └─ B      │ └─ B
 │           │           │
 ├──── A     ├──── C     ├──── C
 │           │           │
 └────── D   └────── D   └────── D

Figure 1. Phylogenetic trees reconstructed from RNA polymerase subunit β (X or Y), transposase (X or Y) and reference genes of ribosomal proteins (Z).

Position I Position II
A GGACT A CAGTC
B CCATT B GCGTC
C GCATA C GCACA
D CGACT D GGCCA

Figure 2. Alignments of representative regions of two genes from four bacteria strains (A-D).

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. Phylogenetic tree X was reconstructed from the alignment I.
B. In the Alignment I, 4 out of 5 positions are useful for determining tree's topology.
C. Phylogenetic tree X was reconstructed from the RNA polymerase subunit β.
D. Using species D as an outgroup, there are in total two possible phylogenetic tree topologies for the four species A-D.
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Question reproduced from IBO 2024, Theoretical Exam Part A, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)