Giardia Intestinalis Can Cause Disease in Several Different Mammalian Species

question 55

Multiple Choice

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. 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. (T. Monis, et al. 1999. Molecular systematics of the parasitic protozoan Giardia intestinalis. Mol. Biol. Evol. 16[9]:1135-44.)
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According to the phylogenetic tree in the figure above, G. intestinalis constitutes a ________ group.

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

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Definitions:

Smell

Refers to the sense that detects chemicals in the environment, allowing for the perception of odors.

Temperament

The innate aspects of an individual's personality, such as introversion or extroversion, often evident from early childhood and influencing behavior.

Teratogens

Agents or factors that cause malformation of an embryo or fetus.

Zygotes

The initial cell formed when a new organism is conceived, resulting from the union of sperm and egg cells.