8
Given below are two statements regarding the neighbor joining method of tree construction, one is labelled as
Assertion (A) : and other one labelled as Reason (R)
Assertion (A) : The neighbor joining method produces a unrooted tree topology, unless an outgroup is specified or midpoint
rooting is applied
Reason (R) : The neighbor joining method assumes a constant rate of evolution.
In light of the above statements, choose the most appropriate answer from the options given below
EXPLANATION
Molecular Phylogenetics
- Neighbor-Joining (NJ) Algorithm Principles:
- Assertion (A): The neighbor joining method produces an unrooted tree topology, unless an outgroup is specified or midpoint rooting is applied. $\implies$ Correct.
- NJ builds an unrooted star-decomposition tree by iteratively joining neighbor pairs that minimize total tree branch length ($S$).
- Reason (R): The neighbor joining method assumes a constant rate of evolution. $\implies$ Incorrect.
- The NJ method does NOT assume an ultrametric tree or a molecular clock (constant evolutionary rate), which is why it was created as an improvement over UPGMA (which strictly assumes equal rates of evolution).
- Conclusion: (A) is correct but (R) is not correct (Option 3).
Explanation not matching this question?
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