The following are steps used to construct a cladogram that best reflects the evolutionary relationships of a group of species. Which step involves deciding which tree is most likely to have occurred, based on the fewest character state changes?

Question

A.  Polarize the characters.
B.  Establish the character states.
C.  Gather data on characters to be used.
D.  Apply the principle of parsimony.
E.  Select an outgroup.


Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?
 
Gather Content
· What do you already know about cladograms?

  Consider Possibilities
· Consider the different answer options. Which can you rule out?

  Choose Answer · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

  Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

D.  Apply the principle of parsimony.

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses cladograms.
· What type of thinking is required?
        o This question is asking you to analyze the information given, using logic, to dissect the problem and determine the answer.
· What key words does the question contain and what do they mean?
        o A cladogram is a diagram that depicts a hypothesis of evolutionary relationships.
        o Character states are the features of an organism, such as presence or absence of hair.
 
Gather Content
· What do you already know about cladograms?
        o A cladogram is a diagram that depicts an evolutionary tree.
        o A simple cladogram is a nested set of clades, each clade characterized by its own synapomorphies.

  Consider Possibilities
· Consider the different answer options. Which can you rule out?
        o Does polarizing the characters decide which tree is most likely? No. Polarizing the characters refers to deciding which is the ancestral and the derived state.
        o Does establishing the character states decide which tree is most likely? No. That means to decide what features to focus on, and what form they take in each species.
        o Does gathering data on characters decide which tree is most likely? No. Again, this is about gathering information about the features of each species.
        o Does selecting an outgroup decide which tree is most likely? No. Selecting an outgroup means to pick the most distantly related species for establishing ancestral character states.

  Choose Answer · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Does applying the principle of parsimony decide which tree is most likely? Yes.
        o The principle of parsimony states that the best hypothesis is the one that requires the fewest  assumptions (divergences).  
        o So the phylogeny that requires the fewest evolutionary events is considered the best hypothesis of phylogenetic relationships when using the principle of parsimony.

  Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked which step of creating a phylogenetic tree helps the researcher decide what is most likely.
        o The question required you to analyze the information given, using logic, to dissect the problem and determine the answer.
        o Did you recognize that when using the principle of parsimony the most likely tree is the one with the fewest character state changes?