Question

The scientists arranged the branches into groups made up of one ancestral variant and all of its descendants, mutated variants. They are color-coded in the figure. Using group 11 as an example, trace the lineage of its variants. (a) Do all of the nodes have the same number of branches or branch tips? (b) Are all of the branches in the group the same length? (c) What do these results indicate?

Short answer

1. Yes, all the nodes of group 11 have an exact number of branches.
2. No, none of the branches of this group have the same length.
3. The exact number of branches represents that the same number of variants has emerged from each common ancestor. On the other hand, the different length of the branches means that the mutation rate was different in these variants.

Step-by-step solution

Explanation for (a)

Node is a common point in the evolutionary tree from where branches are formed.All the nodes of group 11 of the phylogenetic tree have two branches. For instance, variants A/Taiwan/4502/2011 and A/Taiwan/67/2011 diverged from a common ancestor.

Similarly, variants A/Taiwan/4502/2011 and A/Taiwan/67/2011 and variant A/Taiwan/1749/2011 diverged from a common ancestor. Thus, two branches are connected in all the nodes of group 11.

Explanation for (b)

Branches in the evolutionary tree represent the path through which genetic information is transmitted from one generation to another. However, the branch length represents the rate of genetic changes that have occurred in the variants.

All the branches of group 11 have are of different lengths. For instance, the branch length of variant A/Taiwan/4502/2011 is very short compared to the branch length of A/Taiwan/67/2011, which is much longer.

Explanation for (c)

In group 11, all the nodes have the same two branches. This suggests that two variants have emerged from each common ancestor. However, the lengths of the branches are different.

This is because the rate at which mutation occurred and accumulated differs from one variant to another. Thus, the longer the branch, the higher the accumulation of genetic changes in the variants.