Is the positive control considered to be modified crops ? Or is it for negative
ID: 276682 • Letter: I
Question
Is the positive control considered to be modified crops ? Or is it for negative control?
a) An organic farmer states that none of his crops are genetically modified. A student designs a PCR experiment to amplify a 900 bp fragment of the bt endotoxin gene, which is only found in genetically modified plants. He samples ten plants and produces the PCR gel 1 shown below. The labeling indicates a DNA size ladder, positive and negative controls, and ten lanes of samples Gel 1 Gel 2 Samples Samples 1 2 3 45 6 78 9 10 11 12 13 1 2 3 45 6 78 9 10 11 12 13 (i) Based on Gel 1, are any of the ten plants genetically modified? If so, indicate which lanes have samples from genetically modified plants by circling the sample numbers above the lanes in gel 1. Explain your answer (4 marks) (ii) The farmer complains about this result. Looking back at his lab notebook, the student realized that he mislabeled the lanes. The correct labeling is shown in Gel 2. Based on Gel 2, are any of the ten plants genetically modified? Explain your answer. (2 marks)Explanation / Answer
Please find the answers below:
Answer i) According to the image of Gel 1, it can be clearly seen that sample numbers 5, 7, 8, 9, 10 and 11 provide positive results for presence of the genetically modified endotoxin. Hence, it clearly demonstrates that these plant samples have been genetically modified.
Answer ii) After modification of the image, it can be seen that the presence of a band in the positive control suggests that the endotoxin gene is present. Hence, the sample numbers 5, 7, 8, 9, 10, 11 and 13 seem to be genetically modified.
It must be carefully noted here that the relevance has been made between the positive control showing presence of band and the samples. Ideally, a negative control should not give any band since this would mean that no gene has been inserted into the host system.
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