The table shows the distribution of traits (A-E) in six extant species (1-6). A "0" indicates the ancestral condition, and a "1" indicates the derived condition. Which species has the greatest number of ancestral character states (pleisiomorphies)?
A. 1
B. 2
C. 3
D. 4
E. 5
F. 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?
F. 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 Traits are features of an organism, used as data to build a tree.
o Extant species are still alive – i.e., not extinct.
o The ancestral condition of a trait is the original condition; the derived condition is the more newly evolved version.
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.
Consider Possibilities
· What other information is related to the question? Which information is most useful?
o The “1”s are derived characters; the ‘”0”s are ancestral characters.
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
o Species 6 has four “0”s for traits A, B, C, and E, so it has 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 ancestral characters are marked with “0”s in the chart?
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