You are examining the effect of maturation-promoting factor (MPF) in sea urchin cells, which have a diploid number of 36. If you fuse a dividing sea urchin cell with a G1 arrested oocyte, what would be the outcome?

Question

A.  The G1 cell would enter mitosis, but would likely arrest at the spindle checkpoint because the chromosomes have not been properly replicated.  
B.  The G1 cell would undergo mitosis and its daughter cells would each have 36 chromosomes.
C.  The G1 cell would undergo mitosis and its daughter cells would each have 18 chromosomes.
D.  The G1 cell would first go through S phase and then mitosis. Its daughter cells would have 36 chromosomes.

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 know about MPF? How does it relate to the question?

  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

A.  The G1 cell would enter mitosis, but would likely arrest at the spindle checkpoint because the chromosomes have not been properly replicated.  

Clarify Question
  · What is the key concept addressed by the question?
        o The question asks about the effect of maturation promotion factor on a cell in G1.
· What type of thinking is required?
        o You are being asked to analyze different predictions of what would happen if a cell in G1 is fused to a rapidly dividing cell which would express MPF.
· What key words does the question contain and what do they mean?
        o MPF – maturation promoting factor triggers a cell to enter mitosis.
        o Cell arrested in G1 – this cell will not have gone through S phase yet, so its chromosomes will not be replicated.

  Gather Content
  · What do you know about MPF? How does it relate to the question?
        o MPF triggers a cell to enter mitosis.  If a cell has not yet duplicated its chromosomes then spindles will not form properly and the cell will not be able to divide.

  Consider Possibilities  
  · What other information is related to the question? Which information is most useful?
        o While MPF will induce a cell to enter mitosis and not S phase, if the DNA has not replicated then the cell will not be able to split the DNA into equal amounts between the two daughter cells.

Choose Answer
  · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o In the presence of MPF the G1 cell would go immediately into mitosis.  The nuclear envelope would break down, the spindle would assemble and chromosomes would move in the cell.  But because the cell has not gone through S phase, the chromosomes would not be replicated, and thus the cell would likely arrest at the spindle checkpoint.
 
  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 to analyze several predictions of what would happen if a rapidly dividing cell was fused with a cell arrested in G1. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you recall that MPF in the rapidly dividing cell would cause the cell arrested in G1 to immediately enter mitosis without going through S phase?  Did you think that the cell would divide its existing chromosomes without going through S phase?  Did you forget that the checkpoints would prevent cells from dividing if the spindles did not form properly?