The common ancestor shared by mouse and gorilla is at point ______ on the phylogeny shown.

Question

A.  A
B.  B
C.  C
D.  D
E.  E

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 cladistics?
 
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

E.  E

Clarify Question
  · What is the key concept addressed by the question?
        o This question addresses cladistics.
· What type of thinking is required?
        o This question is asking you to take what you already know and apply it to this unfamiliar situation.
· What key words does the question contain and what do they mean?
        o The common ancestor is the ancestor that existed just before the split of the branches.
        o A phylogeny is a diagram describing a hypothesis about evolutionary relationships.
 
Gather Content
· What do you already know about cladistics?
        o Cladistics is the method used to construct a cladogram — a graphically represented hypothesis of evolutionary relationships.
        o Only shared derived characters (synapomorphies) are useful for inferring phylogenies, and they must be contrasted to an outgroup that has the ancestral characters.
        o Each nested clade is defined by a new shared derived character. These new characters are typically labeled on the branch.
 
Consider Possibilities · Consider the different answer options. Which can you rule out?
        o Would the common ancestor of mice and gorillas be below salamanders and newts? No way, those are too distantly related.
        o Would the common ancestor of mice and gorillas be below snakes and lizards? No way, those are too distantly related.
        o Would the common ancestor of mice and gorillas be at C, below the clade of reptiles and mammals? That is an ancestor of mice and gorillas, but not the most recent common ancestor because it was the ancestor of many other species.
        o Would the common ancestor of mice and gorillas be at D, along the branch to mice? No, because that branch did not give rise to gorillas.
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Would the common ancestor of mice and gorillas be at E? Yes, because that is the node below the mammal groups.
 
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 you where the common ancestor of a mouse and gorilla would be on the tree.
        o The question required you to take what you already know and apply it to this unfamiliar situation.
        o Did you recognize that gorillas, mice and chimps are all mammals?