Consider the cladogram shown. If we designate species 1 as the outgroup, which species has the greatest number of ancestral character states (pleisiomorphies)?

Question

A.  2

B.  3

C.  4

D.  5

E.  6





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

· What other information is related to the question? Which information is most useful?

 

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.  6

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 A cladogram is a diagrammatic representation of a hypothesis about evolutionary relationships.
        o Ancestral character traits are those original versions of a trait, before they evolved into something new.
 
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 are useful for inferring phylogenies, and they must be contrasted to an outgroup that has the ancestral characters.
 
Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o A cladogram is a set of nested clades, characterized by their synapomorphies (shared, derived characters).
        o Since the nested clades are defined by synapomorphies, the species in the innermost nested clade – the most closely related species in this cladogram – must share more synapomorphies than more distantly related pairs of species.
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o The outermost species – the outgroup – must have the fewest synapomorphies and the most ancestral states (at least relative to the other species shown in this tree).
        o So species 6 is the one (besides the outgroup, 1) with the most ancestral states.
  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 species has the most ancestral characters.
        o The question required you to take what you already know and apply it to this unfamiliar situation.
        o Did you recognize that the outermost species in the cladogram is most distantly related to the others, and this group has the most ancestral characters?