Potato blight causes potato plants to shrivel and rot. The disease is caused by the pathogen Phytophthora infestans, infamous for its role in Ireland's Great Potato Famine in the mid-1840s. The disease can devastate crops during wet weather, sometimes leading to total crop loss. Researchers aim to use recombinant DNA methods to transfer blight resistance genes from resistant varieties into susceptible varieties of potato.Transgenic plants usually contain genes of bacterial plasmid origin. In a recent study, researchers designed a strategy that avoided using any plasmid genes. They transformed cells from a susceptible potato variety with a potato blight resistance gene cloned from a resistant variety. Next, to determine which plants from this group were also free of plasmid DNA (cloning vector) sequences, they performed PCR using primers specific for the plasmid. The positive control lane shows PCR amplification of plasmid DNA only, and the negative control lane shows an attempted PCR amplification of no added DNA. Based on the gel analysis of PCR products shown below, which plants contain only the potato gene? Explain your answer.

Verified step by step guidance

1. Identify the lanes in the gel that correspond to each plant sample and compare them to the control lanes. The positive control lane should show a band indicating the presence of plasmid DNA, and the negative control should show no bands, indicating no DNA was amplified.
2. Examine the PCR product bands in the lanes for each plant sample. A plant that contains only the potato gene should show a different band pattern compared to the positive control lane, which indicates the presence of plasmid DNA.
3. Check for the absence of bands that match the size and position of the band in the positive control lane in each plant sample. This would suggest that the plasmid DNA is not present in those specific samples.
4. Identify any lanes where the bands match those of the negative control or show a unique pattern that does not correspond to the plasmid DNA band. These samples likely contain only the potato blight resistance gene without any plasmid contamination.
5. Conclude which plants contain only the potato gene by confirming the absence of plasmid DNA bands and the presence of expected bands for the potato blight resistance gene. These plants are the successful transgenic plants with the desired genetic modification.

Key Concepts

Potato Blight and Its Pathogen

Potato blight is a devastating disease caused by the pathogen Phytophthora infestans, which thrives in wet conditions and can lead to significant crop losses. Understanding the biology of this pathogen is crucial for developing resistant potato varieties, as it helps researchers identify the specific genes that confer resistance and the mechanisms by which the disease affects plant health.

Recombinant DNA Technology

Recombinant DNA technology involves combining DNA from different sources to create genetically modified organisms. In this context, researchers are transferring a resistance gene from a blight-resistant potato variety into a susceptible one, which allows for the development of plants that can withstand the disease. This technology is fundamental for improving crop resilience and ensuring food security.

Polymerase Chain Reaction (PCR)

Polymerase Chain Reaction (PCR) is a molecular biology technique used to amplify specific DNA sequences, making it easier to analyze genetic material. In the study, PCR is employed to determine whether the transformed potato plants contain only the resistance gene without any plasmid DNA. The results from PCR help researchers confirm the success of their genetic modifications and the purity of the transgenic plants.