-
Determine the correctness or otherwise of the following Assertion (A) and Reason (R).
Assertion: UPGMA method produces ultrametric tree.
Reason:Sequence alignment is converted into evolutionary distances in UPGMA method.
-
- Both (A) and (R) are true and (R) is the correct reason for (A)
- Both (A) and (R) are true and (R) is not the correct reason for (A)
- (A) is true but (R) is false
- (A) is false but (R) is true
Correct Option: B
The unweighted pair-group method with arithmetic mean (UPGMA) is a popular distance analysis method. UPGMA is the simplest method for constructing trees. The great disadvantage of UPGMA is that it assumes the same evolutionary speed on all lineages, i.e. the rate of mutations is constant over time and for all lineages in the tree. This is called a ‘molecular clock hypothesis’. This would mean that all leaves (terminal nodes) have the same distance from the root. In reality the individual branches are very unlikely to have the same mutation rate. Sequence alignment is converted into evolutionary distances. UPGMA is “ultrametric”, meaning that all the terminal nodes (i.e. the sequences/taxa) are equally distance from the root. In molecular terms, this means that UPGMA assumes a molecular clock, i.e. all lineages are evolving at a constant rate.
