USABO - USA Biology Olympiad Biosystematics and Taxonomy Questions and Answers

Question 1

A biologist classifies a group of organisms based on their shared evolutionary history.
The traditional class "Reptilia" is often cited as an example of a paraphyletic group because it includes lizards, snakes, turtles, and crocodiles, but excludes birds.
What is the defining characteristic of a paraphyletic group?

Accepted Answer

It includes the group's most recent common ancestor but not all of its descendants.

Answer

It is composed of organisms from different evolutionary lineages that do not share a recent common ancestor.

Answer

It represents a group where similar traits have evolved independently in separate lineages.

Answer

It includes the most recent common ancestor and all of its descendants, forming a complete clade.

Question 2

In cladistics, the presence of hair is a key character for defining the clade Mammalia, distinguishing it from other vertebrates. In contrast, the presence of a vertebral column, while common to all mammals, is not a defining character for this specific clade because it is also found in fish, amphibians, and reptiles. How are the vertebral column and hair best described, respectively, in the context of defining Mammalia?

Accepted Answer

Symplesiomorphy; Synapomorphy

Answer

Synapomorphy; Symplesiomorphy

Answer

Autapomorphy; Homoplasy

Answer

Synapomorphy; Autapomorphy

Question 3

A student is writing a report on the fruit fly. According to the formal rules of binomial nomenclature, which of the following is formatted INCORRECTLY?

Accepted Answer

Written in the report as: *Drosophila Melanogaster*

Answer

In the first mention: *Drosophila melanogaster*

Answer

In a subsequent mention: *D. melanogaster*

Answer

Referring to an unspecified species of the genus: *Drosophila* sp.

Question 4

When systematists construct phylogenetic trees, they often evaluate multiple possible trees and select the one that is considered the 'best' hypothesis. The principle of maximum parsimony is a common method for this. Which of the following statements best describes this principle?

Accepted Answer

The preferred tree is the one that requires the fewest evolutionary changes to explain the observed data.

Answer

The most accurate tree is the one that has the most branching points or nodes.

Answer

The tree should be based only on molecular data, as it is more objective than morphology.

Answer

The tree that places the oldest fossil at the root is considered the most parsimonious.

Question 5

A team of biologists is studying a group of plants. Their phylogenetic analysis based on flower morphology suggests that Species A and B are sister taxa. However, an analysis of DNA sequences from the chloroplast genome strongly indicates that Species A is actually most closely related to Species C. What is the most likely evolutionary explanation for this conflict between the morphological and molecular data?

Accepted Answer

The morphological similarities between Species A and B are likely the result of convergent evolution.

Answer

The molecular data must be flawed due to a high rate of mutation in the chloroplast genome.

Answer

Horizontal gene transfer between Species A and C has made their DNA appear artificially similar.

Answer

Morphological data is always a more reliable indicator of evolutionary history than molecular data.

Question 6

The three-domain system, which classifies all life into Bacteria, Archaea, and Eukarya, was established by Carl Woese based on pioneering molecular evidence. What type of molecular data was most critical for revealing that Archaea constitute a domain distinct from Bacteria?

Accepted Answer

Sequence differences in ribosomal RNA (rRNA) genes.

Answer

The structure of proteins involved in DNA replication.

Answer

The composition of lipids in the cell membrane.

Answer

The presence or absence of a peptidoglycan cell wall.