Embryonic cell cycles allow the rapid division of cells in the early embryo. These mitotic cell cycles are much shorter in length than the mitotic cell cycles of cells in a mature organism. In the embryonic cell cycles, mitosis takes approximately the same amount of time as it does in the cell cycles of mature cells. What do you think is a result of the embryonic cycle? 32. Following S phase, a human cell would have how many pairs of sister chromatids and individual DNA molecules?

Question

A.  23 pairs of sister chromatids and 46 individual DNA molecules
B.  23 pairs of sister chromatids and 92 individual DNA molecules
C.  46 pairs of sister chromatids and 46 individual DNA molecules
D.  46 pairs of sister chromatids and 92 individual DNA molecules
E.  46 pairs of sister chromatids and 184 individual DNA molecules

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?


Answer 1

D.  46 pairs of sister chromatids and 92 individual DNA molecules

Clarify Question
  · What is the key concept addressed by the question?
        o The question asks about numbers of chromatids and individual DNA molecules.
· What type of thinking is required?
        o You are being asked to apply your knowledge of chromosomes to predict the numbers of chromatids and DNA molecules after S phase.
· What key words does the question contain and what do they mean?
        o Pairs of sister chromatids –these are formed after replication of the DNA and are attached together to form a single chromosome.
        o Individual DNA molecules – these are separate double stranded DNA molecules.

  Gather Content
  · What do you know about sister chromatids? How does it relate to the question?
        o Sister chromatids form after a chromosome is replicated during S phase.  For each initial chromosome there will now be a pair of sister chromatids.
        o Each pair of sister chromatids then contains two individual DNA molecules that were created from the single DNA molecule before replication in S phase.

  Consider Possibilities  
  · What other information is related to the question? Which information is most useful?
        o A human cell starts with 46 chromosomes.  These are then replicated during S phase.

  Choose Answer
  · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o If a cell starts with 46 chromosomes and replicates in S phase it will produce 46 pairs of sister chromatids.  Each sister chromatid contains two strands of DNA so there will be 92 strands of DNA.

  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 understanding of sister chromatids to calculate how many would be in a human cell after S phase. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you recall that a normal human cell has 46 chromosomes?  Did you understand that each chromosome would produce two sister chromatids after its DNA was replicated?  Did you realize that each sister chromatid was an individual DNA molecule?