Transposable elements are significant features in the genomes of almost all eukaryotic organisms. The accumulation of these elements in various species can help determine their relatedness. Table 1 indicates the presence (+) or absence (−) of 5 segments of DNA that have been moved by transposition (transposons) in 6 primate species.

Table 1. Presence of absence of 5 transposons in primate species
Species 1 2 3 4 5
Human - + + + +
Bonobo + + + + +
Chimpanzee + + + + +
Gorilla - - + + +
Orangutan - - - + +
Gibbon - - - - -

Which of the following best predicts how phylogenetic relationships might be revised if transposon 1 was not found in chimpanzees?

Question

Transposable elements are significant features in the genomes of almost all eukaryotic organisms. The accumulation of these elements in various species can help determine their relatedness. Table 1 indicates the presence (+) or absence (−) of 5 segments of DNA that have been moved by transposition (transposons) in 6 primate species.

Table 1. Presence of absence of 5 transposons in primate species
Species	1	2	3	4	5
Human	-	+	+	+	+
Bonobo	+	+	+	+	+
Chimpanzee	+	+	+	+	+
Gorilla	-	-	+	+	+
Orangutan	-	-	-	+	+
Gibbon	-	-	-	-	-

Which of the following best predicts how phylogenetic relationships might be revised if transposon 1 was not found in chimpanzees?

BlackTom AI · Accepted Answer

Shared transposon insertions are effectively irreversible markers of common ancestry, so a given insertion present in two species usually indicates that their most recent common ancestor carried that insertion.

1) Relevant concepts
- Transposable element insertions are treated as rare, nearly homoplasy-free characters (synapomorphies).
- Presence (+) is a derived state; absence (−) is usually the ancestral state unless independent loss is demonstrated.
- Species that share derived insertions are inferred to be more closely related.

2) Step-by-step reasoning
- Original table: Transposon 1 is present (+) in both bonobo and chimpanzee and absent (−) in human, gorilla, orangutan, gibbon. That pattern supports bonobo+chimpanzee as a clade for insertion 1.
- But if transposon 1 is later found to be absent in chimpanzees, the pattern for transposon 1 becomes: bonobo +, all others −.
- Update the full patterns for the three species of interest:
  - Human: − + + + +
  - Chimpanzee (revised): − + + + +
  - Bonobo: + + + + +
- With that revision, chimpanzee and human have identical presence/absence profiles for transposons 1–5, while bonobo differs by having transposon 1 uniquely.

3) Intermediate observation (no numerical calculation needed)
- Identical profiles for chimpanzee and human across these markers constitute stronger evidence that chimpanzees share a more recent common ancestor with humans than with bonobos for these loci.

4) Why the correct answer is correct
- If only bonobo carries transposon 1, that insertion is an autapomorphy (unique derived character) of bonobo and does not link bonobo to chimpanzee. The shared absence in human and chimpanzee (and identical patterns across transposons 2–5) indicates chimpanzees would group with humans more closely than with bonobos.

5) Why the other options are incorrect
- Chimpanzees being closer to gibbons: gibbons show complete absence of these insertions and are clearly more basal; their profile differs from chimps/humans.
- Orangutans closer to humans than chimps: orangutan’s pattern (− − − + +) differs substantially and does not match humans or chimps.
- Bonobos closer to humans than chimpanzees: bonobo has the unique transposon 1 presence; humans lack it, so bonobo would not be shown as closer to humans than chimpanzees.

6) Conclusion
- Therefore, the best prediction is: Chimpanzees would be more closely related to humans than to bonobos. This matches the provided answer.

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