Question

the figure below shows a phylogenetic tree for some giardia species.
according to the phylogenetic tree in the figure above, what type of evolutionary group does g. intestinalis constitute?

monophyletic
paraphyletic
polyphyletic

Explanation:

Analyze the phylogenetic tree structure

Using the Phylogenetic Trees knowledge point, we trace the common ancestors of the groups.

• The tree shows evolutionary relationships among Giardia muris, Giardia intestinalis (subgroups A, B, C, D), and Giardia microti.
• Subgroups A, B, C, and D are designated as G. intestinalis.
• The most recent common ancestor (MRCA) of all G. intestinalis subgroups (A-D) is located at the node where the lineage leading to A/B/C and the lineage leading to D/G. microti diverge.

Identify the descendants of the common ancestor

• The MRCA of subgroups A, B, C, and D also has Giardia microti as a direct descendant.
• Specifically, subgroup D shares a more recent common ancestor with G. microti than it does with subgroups A, B, or C.

Classify the evolutionary group

• A monophyletic group (clade) must consist of an ancestral species and all of its descendants.
• The group G. intestinalis (subgroups A-D) includes their common ancestor but excludes Giardia microti, which is also a descendant of that same common ancestor.
• A group that consists of a common ancestor and some, but not all, of its descendants is defined as paraphyletic.

Answer:

• monophyletic
• paraphyletic (Correct answer)
• Polyphyletic