Mutation That Most Probably Occurred

¶ … mutation that most probably occurred was a spontaneous mutation. The data support the hypothesis that the mutations are present in the culture prior to exposure to the selective agent. The data found supports that the resistance mutations were spontaneous, meaning that the mutations in the bacteria culture occurred prior to the addition of the selective agent. Spontaneous mutations are standing mutations caused by factors other than the selective agent. These data reprise the Newcombe experiment.

The Newcombe experiment is an experimental technique used in determining whether mutations that make bacterial colonies resistant to virulent phages are spontaneous occurrences or whether exposure of the bacteria to the phage causes the resistance to arise in cells. In this experiment, bacteria are examined and the colony count of surviving colonies is counted. The plates used contained undiluted bacteria exposed to the selective agent, one plate being respread.

When respreading one of the plates and exposing the bacteria to the selective agent, the expected result, if the mutation in the bacteria causing resistance to the selective agent is spontaneous, is that the number of colonies on the respread undiluted colony plate would be higher than that of the original non-respread plates.

The colony number would be expected to be higher because if the plates contain spontaneously resistant bacteria, respreading the plates would then disperse these resistant bacteria and when incubated new resistant colonies would form from these resistant bacteria. From these experimental data, the colony count for the respread plates was higher than that of the non-respread. The mutant concentration on the non-respread undiluted plates was 11750 mutants/ml and 17360 mutants/ml on the respread undiluted E. coli plates.

The mutation causing resistance to the selective agent in the colonies is most likely a missense mutation, a mutation where a nucleotide change in the gene sequence causes a change in protein formation and function. On the other hand, induced mutations are caused by natural or man-made mutagens, which alter the structure or sequence of DNA. The spontaneous mutation frequency, which is the mutants/viable cell, is relatively low.

It is essential to understand the nature of mutations because they contribute to genetic variance in a population to ensure its survival. Bacteria are easy to study because they very short reproductive and life cycles. This lets an observer study multiple generations in a very short period of time. The relatively low frequency of mutations in a population will only result in the survival of a few in the event of a biological calamity.

However, the progeny of the survivors will inherit the mutant strain as well, ensuring the continuity of the species. This would be a boon.