In a 32-cell stage tunicate embryo, vegetal marginal cells that lack functional genes for both macho-1 and the FGF receptor would develop as what cell type?

Question

A.  mesenchyme
B.  muscle
C.  notochord
D.  nerve cord

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 FGF induction?

  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.  nerve cord

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. If they have macho-1 expressed, they become muscle. If not, they become nerve cord.

  Consider Possibilities
· Consider the different answer options. Which can you rule out?         o Would cells lacking FGF receptor and Macho-1 develop into mesenchyme? No, because mesenchyme requires FGF and Macho-1.
        o Would cells lacking FGF receptor and Macho-1 develop into muscle? No, because mesenchyme requires Macho-1.
        o Would cells lacking FGF receptor and Macho-1 develop into notochord? No, because mesenchyme requires FGF.

  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 If they lacked Macho-1, they would develop as if that signal was missing.
        o Would cells lacking FGF receptor and Macho-1 develop into nerve cord? Yes, because nerve cord is the normal outcome when those signals are missing
  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 how cells would develop if the tunicate vegetal  marginal cells lacked FGF receptor and Macho-1.
        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 cell fate that resulted in the absence of FGF and Macho-1 signaling was nerve cord?