Question

To solve the problem below, you must write a clear and convincing justification for accepting one of the possible answer choices as the BEST or MOST APPROPRIATE and for rejecting each of the other choices as less appropriate. Your reasons for rejecting choices are just as important as your reasons for choosing the best answer.

1. A biologist measured the amount of DNA in several single diploid cells taken from a culture. He knew that these cells could divide mitotically, but not meiotically. His data is shown below: Cell Number and DNA content in micrograms: Cell 1 (11.1 micrograms) Cell 2 (5.4 micrograms) Cell 3 (7.3 micrograms) Cell 4 ( 10.9 micrograms) Cell 5 (5.6 micrograms) Cell 6 (8.6 micrograms) Cell 7 (11.0 micrograms) Which of these cells have most likely just completed mitosis and cytokinesis?

a. 1, 4, and 7

b. 3 and 6

c. 2, 3, 5, and 6

d. 2 and 5

e. No conclusion can be drawn from the data provided.

Answer 1

Ans- Option D is correct

The cells in the culture are diploid in nature (2n) and they divide mitotically. The cell cycle goes from:

--G1 phase---S-phase (DNA synthesis)---G 2 Phase---M phase--- Cytokinesis---G1 phase--

The new cells are formed after cytokinesis, it means that these cells will contain the minimum amount of DNA. The DNA content will remain approximately the same till the end of G1-phase and the DNA content starts to increase in S-phase where the DNA synthesis occurs. After the end of S-phase, the DNA content will approximately be the double of G1 phase. Then after this phase, the cell will undergo G2 phase and M-phase where the content of DNA will be the same as S-phase,

Cell No.	Amount of DNA and comments
Cell 1	11.1 ug- This the maximum amount of DNA observed in this experiment. This cell will be probably in G2 or M-phase.
Cell 2	5.4 ug- This is the minimum amount of DNA observed in this experiment. This cell is newly formed after cytokinesis.
Cell 3	7.3 ug- This cell could be in S-phase.
Cell 4	10.9 ug- This cell could be probably in G2 or M-phase.
Cell 5	5.6 ug- This DNA content of this cell is approximately the same to cell 2 so this cell is newly formed after cytokinesis.
Cell 6	8.6 ug- This cell could be in S-phase because the DNA content is in between the maximum and minimum.
Cell 7	11 ug- The DNA content of this cell is closely similar to cell 1. This cell will be probably in G2 or M-phase

So based on the above observations, option D cell 2 and 5 is correct