A somatic cell from a corn plant normally contains 20 chromosomes. How many sister chromatids would that cell contain during G2 of the cell cycle?
A. 0
B. 10
C. 20
D. 40
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 sister chromatids? 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?
D. 40
Clarify Question
· What is the key concept addressed by the question?
o The question asks about the number of sister chromatids in G2.
· What type of thinking is required?
o You are being asked to apply your knowledge of the cell cycle to predict how many sister chromatids there are in G2.
· What key words does the question contain and what do they mean?
o G2 of the cell cycle – this is after S phase of the cell cycle so the DNA has been replicated.
o Sister chromatids – these form after the DNA is replicated in S phase but before they separate in mitosis. The two sister chromatids comprise a single chromosome.
Gather Content
· What do you know about sister chromatids? How does it relate to the question?
o Sister chromatids form after the DNA is replicated in S phase but before they separate in mitosis.
Consider Possibilities
· What other information is related to the question? Which information is most useful?
o If a somatic cell contains 20 chromosomes, this will be the diploid number. The haploid number will be 10. If the cell had gone through mitosis and entered G1 then there would be 0 sister chromatids.
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
o Because the cell is in G2 it will have replicated its DNA and will have two sister chromatids per chromosome. Since there are 20 chromosomes there will be 40 sister chromatids.
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 apply your knowledge of when chromosomes replicate to form sister chromatids. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you recall that DNA replicates in S phase before G2 so there would be two sister chromatids per chromosome? Did you think that the sister chromatids had already separated in mitosis which actually occurs after G2?
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