Evolution Lab Report
4. Results
No hypotheses in the discussion section were necessarily falsified, but some broad statements were made. For example; “Culture conditions obviously influence the outcome of adaptive evolution.” This statement implies that they have extensive knowledge on all the different aspects of evolution. Many scientists today will admit that we do not fully understand evolution and all the factors involved. To say that the conditions ‘obviously’ influenced that outcome is too broad of a statement considering we weren’t there to see most of earth’s evolution take place.
In the introduction, Gauge assumed that either tryptophan negative, or weak tryptophan positive genes would survive in a tryptophan-free environment. Gauge was proved correct when one of the E.coli strains carrying the mutated tryptophan gene was unable to grow. However, one of the mutated E.coli genes was proved to be weakly tryptophan producing and appeared only one week after inoculation. This result showed that the E.coli bacteria are able to survive under low tryptophan conditions. With this result, Gauge …show more content…
claims that the bacteria should still want to mutate in order to receive high levels or tryptophan production.
Another hypothesis that is made is based on the phenotypes of the E.coli bacteria; two different strands with separate trpA mutations. Based on these two mutations, it was inferred that if a cell had both mutations in it’s genes, it should be able to attain full tryptophan synthesis by an adaptive pathway: trpAE49V,D60N → trpAD60N → trpA
The first step, reversion of E49V, would produce the weak Trp+ phenotype of trpAD60N, which presumably carries a fitness advadtage relative to the initial Trp– double-mutant strain. That selective advantage should allow the trpAD60N allele to become fixed, at which point the wild-type trpA revertant would soon follow and, based on its large fitness advantage, quickly overtake the culture.1
This excerpt from the research paper displays some of the bold assumptions made by Gauge. Here, Gauge is claiming that this is the exact pathway that E.coli have to take in order to prove that adaptive evolution takes place. In reality, there is no way to stimulate or predict a change in a population. This research paper seems to claim that the only evolution that could even be possible is adaptive and in response to an environmental stressor, they choose to dismiss the idea of chance and spontaneous changes.
5. Discussion/Conclusions
The paper states that the topic of metabolic costs are almost always overlooked when it comes to the discussion of evolution or natural selection, and that they don’t see how such a radical idea could be favored. It was concluded in the study, that the tryptophan gene mutations did not revert back to fully tryptophan producing genes under reduced tryptophan levels. For a statement this broad to be made, many more trials and experiments should be completed because adaptive evolution is fashioned by different interactions including; population genetics, natural selection and underlying network and biochemical restraints.3
Even though the E.coli with two mutations didn’t regain full tryptophan production in the trials that were done, it doesn’t mean that it couldn’t have happened overtime. Many of the mutants in this study were able to revert one of their mutations, showing that there was some adaptations taking place. Just because none of the mutants were able to acquire two favorable mutations, doesn’t necessarily mean it is impossible. Evolutionary changes happen over periods of thousands, even millions of years, it would be naïve to assume that mutations in the bacteria would happen on a researches preferred timeline. On top of this, you can’t predict a specific adaptive change that might happen in a population. Any mutation could have potentially taken place in the E.coli experiment, not just ones pertaining to tryptophan.
One specific claim made in the discussion pertains to molecular biology research and its claims on proteins used in gene recruitment. Gene recruitment is when a gene becomes recruited to use for another function. This phenomenon is used to support the theory of evolution when organisms are able to adapt a gene for a use that is more beneficial.2
We recognize that the kind of over-expression that we describe here is unlikely to be selected for or maintained by cells in nature because of its fitness cost. However, this scenario is routinely adopted in studies of gene recruitment.1
Despite their claim that this phenomenon is unrealistic, there are many documented cases of genes having adapted functions. These genes are present in many mammals, birds, reptiles, even marine invertebrates.1 The paper is once again making a broad statement based an outcome of a single experiment.
At the end of the discussion, the paper claims that populations of cells were grown slowly under nutrient limiting conditions. They believe this allowed for many possible pathways that could be taken to achieve higher fitness. When the cells did not take the multi-step pathway that was predicted, it seemingly determined that the cost of expressing genes puts momentous constraint on the probability of new functions emerging. In result of this, it was concluded that populations are unlikely to take an adaptive path to high fitness if the path requires over-expression. However, earlier in the introduction it was stated that the only probable to have a new functions emerge is by the over-expression of mutations.
In experimental evolution, the best way to permit various evolutionary alternatives, and assess their relative likelihood, is to avoid conditions that rule them out.1
Based on the result, it is decided in the discussion that adaptive evolution is a less probable scenario and that evolutionary alternatives should not be ruled out.
What the researches of this study failed to recognize that natural selection and evolution are an extremely complicated process and they will not always work the way you believe they will. According the University of Alberta, if bacteria were able to revert from two or more mutations, these bacterial cells would have an unusually high mutation rate.4 This means that it would actually be unlikely for the E.coli mutants to revert back to a fully tryptophan-producing pathway.
6. Weaknesses
Based on the methods, the procedures completed in this experiment comply with microbiology protocols.
Nevertheless, In order to improve this experiment, multiple aspects could be altered. The first thing that would need to be changed is the amount of time and generations of bacteria. Since evolution is based on the premise of mutations according by chance, you cannot assume that a mutation is going to occur at any specific time. Also, based on the methods, there seems to have only been one large trial consisting of many cultures from the same liquid medium. Even though multiple generations of E.coli were grown, the procedure was never repeated in its entirety. I believe evolution and spontaneous change take time and chance, and require would multiple trials. The researchers in this particular experiment only completed one trial then immediately characterized evolution as near
impossible.
The paper has also failed to recognize that evolutionary change doesn’t always function as expected. There was never any discussion about chance or spontaneous change discussed in evolutionary theory, which would have been tightly tied to this specific research. In addition to this, the research was also unable to test for any unknown mutations occurring in the population. Many other genes in the population could have been altered in response to the low tryptophan conditions or spontaneously.
7. Implications
The idea of mutating genes in E.coli could be beneficial to medical and microbiology studies. Due to the antibiotic resistance of E.coli, it could be beneficial to see how it reacts to mutations in its genes. It could also be beneficial to compare mutation rates between populations of bacterial E.coli or other prokaryotic cells. In addition to adaptive evolutionary theory, this research could be related to gene recruitment, mutation rates, and other evolutionary concepts. 8. Other (optional)
As previously stated, Gauger essentially came up with a mediocre experiment and generated fallacious conclusions attempting to disprove evolution.
No hypotheses in the discussion section were necessarily falsified, but some broad statements were made. For example; “Culture conditions obviously influence the outcome of adaptive evolution.” This statement implies that they have extensive knowledge on all the different aspects of evolution. Many scientists today will admit that we do not fully understand evolution and all the factors involved. To say that the conditions ‘obviously’ influenced that outcome is too broad of a statement considering we weren’t there to see most of earth’s evolution take place.
In the introduction, Gauge assumed that either tryptophan negative, or weak tryptophan positive genes would survive in a tryptophan-free environment. Gauge was proved correct when one of the E.coli strains carrying the mutated tryptophan gene was unable to grow. However, one of the mutated E.coli genes was proved to be weakly tryptophan producing and appeared only one week after inoculation. This result showed that the E.coli bacteria are able to survive under low tryptophan conditions. With this result, Gauge …show more content…
claims that the bacteria should still want to mutate in order to receive high levels or tryptophan production.
Another hypothesis that is made is based on the phenotypes of the E.coli bacteria; two different strands with separate trpA mutations. Based on these two mutations, it was inferred that if a cell had both mutations in it’s genes, it should be able to attain full tryptophan synthesis by an adaptive pathway: trpAE49V,D60N → trpAD60N → trpA
The first step, reversion of E49V, would produce the weak Trp+ phenotype of trpAD60N, which presumably carries a fitness advadtage relative to the initial Trp– double-mutant strain. That selective advantage should allow the trpAD60N allele to become fixed, at which point the wild-type trpA revertant would soon follow and, based on its large fitness advantage, quickly overtake the culture.1
This excerpt from the research paper displays some of the bold assumptions made by Gauge. Here, Gauge is claiming that this is the exact pathway that E.coli have to take in order to prove that adaptive evolution takes place. In reality, there is no way to stimulate or predict a change in a population. This research paper seems to claim that the only evolution that could even be possible is adaptive and in response to an environmental stressor, they choose to dismiss the idea of chance and spontaneous changes.
5. Discussion/Conclusions
The paper states that the topic of metabolic costs are almost always overlooked when it comes to the discussion of evolution or natural selection, and that they don’t see how such a radical idea could be favored. It was concluded in the study, that the tryptophan gene mutations did not revert back to fully tryptophan producing genes under reduced tryptophan levels. For a statement this broad to be made, many more trials and experiments should be completed because adaptive evolution is fashioned by different interactions including; population genetics, natural selection and underlying network and biochemical restraints.3
Even though the E.coli with two mutations didn’t regain full tryptophan production in the trials that were done, it doesn’t mean that it couldn’t have happened overtime. Many of the mutants in this study were able to revert one of their mutations, showing that there was some adaptations taking place. Just because none of the mutants were able to acquire two favorable mutations, doesn’t necessarily mean it is impossible. Evolutionary changes happen over periods of thousands, even millions of years, it would be naïve to assume that mutations in the bacteria would happen on a researches preferred timeline. On top of this, you can’t predict a specific adaptive change that might happen in a population. Any mutation could have potentially taken place in the E.coli experiment, not just ones pertaining to tryptophan.
One specific claim made in the discussion pertains to molecular biology research and its claims on proteins used in gene recruitment. Gene recruitment is when a gene becomes recruited to use for another function. This phenomenon is used to support the theory of evolution when organisms are able to adapt a gene for a use that is more beneficial.2
We recognize that the kind of over-expression that we describe here is unlikely to be selected for or maintained by cells in nature because of its fitness cost. However, this scenario is routinely adopted in studies of gene recruitment.1
Despite their claim that this phenomenon is unrealistic, there are many documented cases of genes having adapted functions. These genes are present in many mammals, birds, reptiles, even marine invertebrates.1 The paper is once again making a broad statement based an outcome of a single experiment.
At the end of the discussion, the paper claims that populations of cells were grown slowly under nutrient limiting conditions. They believe this allowed for many possible pathways that could be taken to achieve higher fitness. When the cells did not take the multi-step pathway that was predicted, it seemingly determined that the cost of expressing genes puts momentous constraint on the probability of new functions emerging. In result of this, it was concluded that populations are unlikely to take an adaptive path to high fitness if the path requires over-expression. However, earlier in the introduction it was stated that the only probable to have a new functions emerge is by the over-expression of mutations.
In experimental evolution, the best way to permit various evolutionary alternatives, and assess their relative likelihood, is to avoid conditions that rule them out.1
Based on the result, it is decided in the discussion that adaptive evolution is a less probable scenario and that evolutionary alternatives should not be ruled out.
What the researches of this study failed to recognize that natural selection and evolution are an extremely complicated process and they will not always work the way you believe they will. According the University of Alberta, if bacteria were able to revert from two or more mutations, these bacterial cells would have an unusually high mutation rate.4 This means that it would actually be unlikely for the E.coli mutants to revert back to a fully tryptophan-producing pathway.
6. Weaknesses
Based on the methods, the procedures completed in this experiment comply with microbiology protocols.
Nevertheless, In order to improve this experiment, multiple aspects could be altered. The first thing that would need to be changed is the amount of time and generations of bacteria. Since evolution is based on the premise of mutations according by chance, you cannot assume that a mutation is going to occur at any specific time. Also, based on the methods, there seems to have only been one large trial consisting of many cultures from the same liquid medium. Even though multiple generations of E.coli were grown, the procedure was never repeated in its entirety. I believe evolution and spontaneous change take time and chance, and require would multiple trials. The researchers in this particular experiment only completed one trial then immediately characterized evolution as near
impossible.
The paper has also failed to recognize that evolutionary change doesn’t always function as expected. There was never any discussion about chance or spontaneous change discussed in evolutionary theory, which would have been tightly tied to this specific research. In addition to this, the research was also unable to test for any unknown mutations occurring in the population. Many other genes in the population could have been altered in response to the low tryptophan conditions or spontaneously.
7. Implications
The idea of mutating genes in E.coli could be beneficial to medical and microbiology studies. Due to the antibiotic resistance of E.coli, it could be beneficial to see how it reacts to mutations in its genes. It could also be beneficial to compare mutation rates between populations of bacterial E.coli or other prokaryotic cells. In addition to adaptive evolutionary theory, this research could be related to gene recruitment, mutation rates, and other evolutionary concepts. 8. Other (optional)
As previously stated, Gauger essentially came up with a mediocre experiment and generated fallacious conclusions attempting to disprove evolution.