Natural Selection Lab Report

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Natural selection is a powerful evolutionary mechanism. Mutations are the most important source of variety on which natural selection depends and operates. Mutation and selection work together to bring about evolutionary change. Bacteria provide an ideal system to study evolution because they reproduce quickly and asexually, they permit the study of large sample sizes, they are easy to propagate and it is easy to manipulate their environment. We will be discussing about a common soil bacterium, Bacillus thuringiensis. We will be looking into selection experiment and the results obtained of the bacterium. The goals of this experiment are to observe evolution in real time through the process of mutation and natural selection and to gain an appreciation…show more content…
thuringiensis, evolves resistance to the antibiotic streptomycin. The drug typically retard bacterial proliferation by entering the microbes and interfering with the production of components needed to form bacterial cells. Here we took the bacterial strain that is initially susceptible to the antibiotic streptomycin and carry out selection experiment that allows the evolution of resistant strain. Specifically, we streak the bacterium, B. thuringiensis on three different plates, one nutrient agar plate, one nutrient agar plate with streptomycin antibiotic and a gradient plate with one side of plate having high amount and another with low amount of streptomycin. All the plates will be incubated at 37 degree Celsius overnight. The gradient plate closest to high side will be restreaked twice on another gradient plate. After three rounds of selection, another control and streptomycin plate will be streaked with the bacteria from the latest gradient plate at high side then incubated again overnight. We expect to see an increase in bacterial growth in the selected streptomycin antibiotic plate culture showing us that the bacterium now has resistance to the streptomycin antibiotic. This has been previously observed in other organisms such as Staphylococcus aureus which responded poorly to a once reliable antidote that is the antibiotic…show more content…
We can infer that most of the bacteria are highly susceptible to streptomycin will die but bacterial cells that have some resistance from the start are able to survived. Our selected streptomycin plate has more growth compared to our original streptomycin plate. Cells that previously have some streptomycin resistance from the start, survived and will spontaneously produce a new resistance trait or will strengthen an existing one during cell division through genetic mutation. Our original control plate has more growth than our selected control plate. Our original control plate has both susceptible bacteria cells and resistant cells but with the selected control plate, there is only growth of resistant strains. These results suggest that initially the bacteria are highly susceptible to the streptomycin antibiotics but cells that have some resistance from the start may survive. Those cells facing reduced competition from susceptible bacteria will then go on to

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