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Ch. 1 - The Microbial World and You
Chapter 1, Problem 10.3a

DRAW IT Use the following rRNA information to construct a cladogram for some of the organisms used in question 4. What is the purpose of a cladogram? How does your cladogram differ from a dichotomous key for these organisms?
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Understand the purpose of a cladogram: A cladogram is a diagram that shows the evolutionary relationships among a group of organisms. It is based on the concept of shared derived characteristics and helps to illustrate the branching patterns of evolution.
Examine the rRNA information provided: rRNA sequences are often used in constructing cladograms because they are highly conserved and can provide insights into evolutionary relationships. Look for similarities and differences in the rRNA sequences of the organisms.
Identify shared derived characteristics: Determine which organisms share specific rRNA sequence features that indicate a common ancestor. These shared characteristics will help you group the organisms into clades.
Construct the cladogram: Start with the most ancestral organism and branch out to show the evolutionary relationships based on the shared derived characteristics identified. Each branch point, or node, represents a common ancestor shared by the organisms on that branch.
Differentiate from a dichotomous key: A cladogram shows evolutionary relationships and is based on genetic information, while a dichotomous key is a tool used for identifying organisms based on physical characteristics and does not imply evolutionary relationships.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Cladogram

A cladogram is a diagram that represents the evolutionary relationships among various biological species based on shared characteristics, often derived from genetic data such as rRNA sequences. It illustrates how species diverged from common ancestors, allowing scientists to visualize evolutionary pathways and the relative timing of these divergences.

Dichotomous Key

A dichotomous key is a tool used for identifying organisms based on a series of choices that lead the user to the correct name of a given item. Each step presents two contrasting statements about the organism's characteristics, guiding the user through a systematic process to arrive at the identification, unlike a cladogram which focuses on evolutionary relationships.
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rRNA Sequences

Ribosomal RNA (rRNA) sequences are crucial for understanding the phylogenetic relationships among organisms, as they are highly conserved and present in all living cells. By comparing rRNA sequences, scientists can infer evolutionary relationships and construct cladograms that reflect the genetic similarities and differences among species, providing insights into their evolutionary history.
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Related Practice
Textbook Question

Bergey’s Manual of Systematics of Archaea and Bacteria differs from Bergey’s Manual of Determinative Bacteriology in that the former

a. groups bacteria into species.

b. groups bacteria according to phylogenetic relationships.

c. groups bacteria according to pathogenic properties.

d. groups bacteria into 19 species.

e. all of the above

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Textbook Question

Bacillus and Lactobacillus are not in the same order. This indicates that which one of the following is not sufficient to assign an organism to a taxon?

a. biochemical characteristics

b. amino acid sequencing

c. phage typing

d. serology

e. morphological characteristics

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Textbook Question

Which of the following is used to classify organisms into the Kingdom Fungi?

a. ability to photosynthesize; possess a cell wall

b. unicellular; possess cell wall; prokaryotic

c. unicellular; lacking cell wall; eukaryotic

d. absorptive; possess cell wall; eukaryotic

e. ingestive; lacking cell wall; multicellular; prokaryotic

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Textbook Question

Which of the following is false about scientific nomenclature?

a. Each name is specific.

b. Names vary with geographical location.

c. The names are standardized.

d. Each name consists of a genus and specific epithet.

e. It was first designed by Linnaeus.

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Textbook Question

DRAW IT Use the information in the following table to complete the dichotomous key to these organisms. What is the purpose of a dichotomous key? Look up each genus in Chapter 11, and provide an example of why this organism is of interest to humans.

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Textbook Question

You could identify an unknown bacterium by all of the following except

a. hybridizing a DNA probe from a known bacterium with the unknown’s DNA.

b. making a fatty acid profile of the unknown.

c. specific antiserum agglutinating the unknown.

d. ribosomal RNA sequencing.

e. percentage of guanine + cytosine.

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