A cell biologist produces a karyotype of mouse somatic cells arrested in mitosis. She sees 40 chromosomes, which is completely normal for mice. Based on this information, what is the haploid number of chromosomes for mice?

Question

A.  10
B.  20
C.  40
D.  80
E.  It cannot be determined from the information provided

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 diploid cells? 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

B.  20

Clarify Question
  · What is the key concept addressed by the question?
        o The question asks about predicting the number of chromosomes in a haploid cell.
· What type of thinking is required?
        o You are being asked to apply your knowledge of diploid cells to calculate the number of chromosomes in a haploid cell.
· What key words does the question contain and what do they mean?
        o Somatic cell arrested in mitosis – this is a normal cell in the mouse which would be diploid.

  Gather Content
  · What do you know about diploid cells? How does it relate to the question?
        o The karyotype was done with somatic cells arrested in mitosis.  The 40 chromosomes observed represents the diploid number (2n).  

  Consider Possibilities  
  · What other information is related to the question? Which information is most useful?
        o If there are 40 chromosomes in a diploid cell then 80 chromosomes would be tetraploid.  10 chromosomes would be half the number in a haploid cell and would not occur naturally.

  Choose Answer
  · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o The haploid number (n) will be half the number of chromosomes that was observed in the diploid cell (2n).  Therefore, the haploid number is 20.

  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 the definitions of haploid and diploid to calculate the number of chromosomes in a haploid cell. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you remember the definitions of haploid and diploid?  Did you recognize that the somatic cell was diploid?  Did you know how to calculate the number of chromosomes in a haploid cell if you knew the number in a diploid cell?