Homework SourseI need help understanding how to work through the generation
I need help understanding how to work through the generations and how I would fill in the tables?
| Generation | ?Both strands heavy (15/15) | One strand heavy(15/14) | Neither strand heavy (14/14) |
|---|---|---|---|
| 1 | |||
| 2 | |||
| 3 | |||
| 4 | |||
| 6 | |||
| 8 |
Solution
There is a twist in the question; I do not know if it is deliberate or a mistake. The Messelson-Stahl experiment used N15 medium. DNA normally contains N14. In the given question, if we use N15 medium, then all DNA in all cases will only be N15 (i.e. 15/15) type. Therefore, I am solving the questions assuming that the medium is N14, not N15.
Conservative
In the conservative model, the parent DNA forms two daughter DNA molecules, such that one molecule is identical to the parent DNA. You may also think of this as one parent DNA molecule produces one daughter molecule. The medium contains N14. So, in the first cycle, one N14 (14/14) will be produced. Thereafter, all other DNA molecules produced will be N14 (14/14). Only one parent strand will be N15 (15/15) and no N14.5 (15/14) will be produced.
Generation
Both strands heavy (15/15)
One strand heavy (15/14)
Neither strand heavy (14/14)
1
1
0
1
2
1
0
3
3
1
0
7
4
1
0
15
6
1
0
31
8
1
0
127
Semi-conservative
In the semi-conservative model, the parent DNA forms two daughter DNA molecules, such that both molecules retain one parental strand. So, in the first cycle, two N14.5 (15/14) will be produced. Thereafter, all other DNA molecules produced will be N14 (14/14).
Generation
Both strands heavy (15/15)
One strand heavy (15/14)
Neither strand heavy (14/14)
1
0
2
0
2
0
2
2
3
0
2
6
4
0
2
14
6
0
2
30
8
0
2
126
| Generation | Both strands heavy (15/15) | One strand heavy (15/14) | Neither strand heavy (14/14) |
| 1 | 1 | 0 | 1 |
| 2 | 1 | 0 | 3 |
| 3 | 1 | 0 | 7 |
| 4 | 1 | 0 | 15 |
| 6 | 1 | 0 | 31 |
| 8 | 1 | 0 | 127 |
