In a 32-cell stage tunicate embryo, if the vegetal marginal cells lack a functional FGF receptor, which structure(s) will fail to develop? (Select all that apply)A) notochordB) mesenchymeC) muscleD) nerve cord
What will be an ideal response?
A, B
Clarify Question
• What is the key concept addressed by the question?
o This question addresses FGF induction.
• 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 Tunicates are marine invertebrates also known as sea squirts.
o The vegetal marginal cells lie on the edge of the vegetal pole and can respond to the FGF signal, and eventually make either mesenchyme or notochord.
Gather Content
• What do you already know about FGF induction?
o The example of induction in the vegetal marginal cells of tunicates illustrates how different cells can have different responses to the same inductive signal, depending on what other genes are active in the cell.
o If the vegetal marginal cells receive the FGF signal and also have the Macho-1 gene expressed, those cells will become mesenchyme.
o If the vegetal marginal cells receive the FGF signal but do not have the Macho-1 gene expressed, those cells will become notochord.
o If the cells did not receive the FGF signal, they would become either muscle or nerve cord.
Consider Possibilities
• Consider the different answer options. Which can you rule out?
o Would cells lacking FGF receptor fail to make muscle or nerve cord? No, because those normally result when the FGF signal is not received.
Choose Answer
• Given what you now know, what information and/or problem-solving approach is most likely to produce the correct answer?
o If the cells lacked the FGF receptor, they would not be able to receive the FGF signal, and would develop as if there were no signal.
o They would not be able to develop into the fates that depend on the FGF signal-notochord and mesenchyme.
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 cells would fail to develop if the tunicate vegetal marginal cells lacked FGF receptor.
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 the two cell fates that depended on FGF were mesenchyme and notochord?
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What will be an ideal response?
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