Discussion

After analysis of the results, you decided that there were four problems with Dr. Gen E. Tics' Mutagens Only Hypothesis:

  1. The growth on the ampicillin plate did not agree with the hypothesis.
  2. The growth on the Trp minimal plate did not agree with the hypothesis.
  3. The growth on the His minimal plate did not agree with the hypothesis.
  4. The growth on the Trp and His minimal plate did not agree with the hypothesis.

Disproving The Mutagens Only Hypothesis

Comparision Of The Ampicillin Plate To The Master Culture

The only difference between the master plate and the ampicillin plate is the presence of the antibiotic on the second plate. If the doctor was right and the E colisample was not exposed to any mutagens, then no mutants should exist and the genetic information should be identical in all cells. Therefore, all cells should either be resistant or sensitive to the antibiotic. If the cells were resistant, than the ampicillin plate should be identical to the master plate. If the cells were sensitive, then the ampicillin plate should be empty.

Yet, this was not the result. The ampicillin plate was not identical to the master plate and it was not empty. Three colonies were found to exist on the plate indicating that three colonies were resistant to the antibiotic. You concluded that a mutation must have occurred in these cells giving them ampicillin resistance allowing them to survive on the plate where the majority of cells could not.

Comparision Of The Minimal Mediums To The Master Culture

If the doctor was right, all the cultures grown on the minimal mediums should all be identical to each other and the control plate. If the E. coli sample was not exposed to any mutagens, then no mutants should exit and the genetic information should be identical in all the E. coli cells. Therefore, all cells should be able to metabolize and synthesize the same nutrients and growth should be identical on all the plates.

Yet, the plates were not identical to each other or the control plate. The was one colony missing from the Trp minimal plate, one colony missing from the His minimal plate and three colonies missing from the His and Trp minimal plate, as shown in the below:
E. coli grown on control plate for 24h at 37°C. E. coli grown on Trp minimal plate for 24h at 37°C.
E. coli grown on His minimal plate for 24h at 37°C. E. coli grown on His and Trp minimal plate for 24h at 37°C.

You conclude the following about each of the plates:

The Trp Minimal Plate:
The colony missing on the Trp minimal plate has lost the ability to synthesize Trp. Because Trp is not available from the environment to meet the needs of the cells in the colony, they die.
The His Minimal Plate:
The colony missing on the His minimal plate has lost the ability to synthesize His. Because His is not available from the environment to meet the needs of the cells in the colony, they die.
The His and Trp Minimal Plate:
The A colony missing on the His and Trp minimal plate is the same as the colony missing on the Trp minimal plate. It has lost the ability to synthesize Trp. Because Trp is not available from the environment to meet the needs of the cells in the colony, they die.
The B colony missing on the His and Trp minimal plate is the same as the colony missing on the His minimal plate. It has lost the ability to synthesize His. Because His is not available from the environment to meet the needs of the cells in the colony, they die.
The C colony missing on the His and Trp minimal plate has lost the ability to synthesize His and Trp. Because neither His nor Trp are available from the environment to meet the needs of the cells in the colony, they die.

You write down your conclusions and send them to Dr. Gene E. Tics so that he might understand his mistakes. (Click on the Outcome button in the left margin)