Figure 29.1 Use the Following Information to Answer the Corresponding Question(s)

question 20

Multiple Choice

Figure 29.1
Use the following information to answer the corresponding question(s) .
Giardia intestinalis can cause disease in several different mammalian species,including humans.Giardia organisms (G.intestinalis) that infect humans are similar morphologically to those that infect other mammals;thus they have been considered a single species,though other species in the Giardia genus infect other organisms.However,G.intestinalis has been divided into different subgroups based on their host and a few other characteristics.
In 1999,a DNA sequence comparison study tested the hypothesis that these subgroups actually constitute different species.The following phylogenetic tree was constructed from the sequence comparison of rRNA from several subgroups of G.intestinalis and a few other morphologically distinct species of Giardia.The researchers concluded that the subgroups of Giardia are sufficiently different from one another genetically that they could be considered different species.

-According to the phylogenetic tree in Figure 29.1,Giardia intestinalis constitutes a _____ group.

• A)paraphyletic
• B)monophyletic
• C)polyphyletic