A geneticist examines a somatic cell from a fly during metaphase of mitosis and determines that 16 chromatids are present. If a germ-line cell from this species divides by meiosis, then at the end of meiosis I (including the first cytokinesis) each cell will contain

Question

A.  8 chromosomes with 8 DNA molecules.
B.  8 chromosomes with 16 DNA molecules.
C.  4 chromosomes with 4 DNA molecules.
D.  4 chromosomes with 8 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 meiosis? 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.  4 chromosomes with 8 DNA molecules.


Clarify Question
  · What is the key concept addressed by the question?
        o The question asks about the number of chromosomes present in a cell after meiosis I.
· What type of thinking is required?
        o You are being asked to calculate the number of chromosomes present in a cell after meiosis.
· What key words does the question contain and what do they mean?
        o A cell in metaphase of mitosis has 16 chromatids – there are two chromatids in a chromosome after going through S phase.

  Gather Content
  · What do you know about meiosis? How does it relate to the question?
        o If a diploid cell has 16 chromatids, these will consist of 8 pairs of sister chromatids which each make a chromosome.
        o In meiosis I chromosome pairs align and then separate. So after meiosis I the cells will be diploid, containing one copy of each chromosome.

Consider Possibilities  
· What other information is related to the question? Which information is most useful?
        o Each chromosome after meiosis I consists of two 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 If the cell has 16 chromatids during metaphase of mitosis, this means the diploid number of the cell is 8 chromosomes. After meiosis I the cells will now be haploid with 4 chromosomes.
        o In metaphase I of meiosis, the chromosome pairs each align. As each chromosome contains a pair of sister chromatids, this forms a tetrad. After meiosis I the cells will now be haploid, but each chromosome will contain two chromatids. So for each chromosome there will be two DNA molecules, so the 4 chromosomes will contain 8 DNA molecules.

  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 a problem to calculate the number of chromosomes and DNA molecules in a cell after meiosis I. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you understand that the diploid number would be 8 chromosomes? Could you calculate that after meiosis I the cell would now be haploid with 4 chromosomes? Did you understand that each chromosome would contain 2 sister chromatids, meaning the cell has 8 DNA molecules?