Question

question 6
1 pts
in a phylogenetic tree, the most recent common ancestor (mrca) of all the organisms in the tree would be found
at the top left of the tree.
at the branch point just above the root (bottom) of the tree.
at the top right of the tree.
at the branch point just below two of the organisms listed across the top of the tree.

Explanation:

A phylogenetic tree's root represents the oldest common ancestor, and the MRCA of all organisms in the tree is the common ancestor from which all the organisms in the tree diverged. The root is at the bottom, and the MRCA of all organisms would be at the branch point just above the root (since the root is the oldest, the MRCA of all in the tree is the common ancestor that is the starting point for all the lineages in the tree, which is just above the root). The other options are incorrect: top left/right are tips or more recent branches, and the branch point below two top organisms is a more recent common ancestor for just those two, not all.

Answer:

B. at the branch point just above the root (bottom) of the tree.