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. Step 1: Understand the problem. The question is asking us to identify which plants contain only the potato gene, based on the gel analysis of PCR products. PCR, or Polymerase Chain Reaction, is a technique used to amplify a specific DNA sequence. In this case, the researchers are using PCR to determine if the plants contain any plasmid DNA sequences.
2. Step 2: Understand the controls. The positive control lane shows PCR amplification of plasmid DNA only. This means that if a plant contains plasmid DNA, its PCR product will look similar to the positive control. The negative control lane shows an attempted PCR amplification of no added DNA. This means that if a plant does not contain any DNA, its PCR product will look similar to the negative control.
3. Step 3: Analyze the gel. The gel analysis of PCR products will show bands representing the DNA sequences that were amplified. If a plant contains only the potato gene, its PCR product will not show a band in the same position as the positive control, because it does not contain any plasmid DNA.
4. Step 4: Identify the plants. The plants that contain only the potato gene are the ones whose PCR products do not show a band in the same position as the positive control. These plants are free of plasmid DNA sequences.
5. Step 5: Explain your answer. The plants that contain only the potato gene do not show a band in the same position as the positive control because they do not contain any plasmid DNA. This is confirmed by the fact that their PCR products look different from the positive control, which shows PCR amplification of plasmid DNA only.

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. The historical context of the Great Potato Famine highlights the importance of addressing this disease to ensure food security.

Recombinant DNA Technology

Recombinant DNA technology involves combining DNA from different sources to create genetically modified organisms. In this case, researchers aim to transfer a blight resistance gene from a resistant potato variety into a susceptible one. This process often utilizes plasmids as vectors, but the study mentioned seeks to avoid plasmid DNA, focusing solely on the potato gene.

Polymerase Chain Reaction (PCR)

Polymerase Chain Reaction (PCR) is a molecular biology technique used to amplify specific DNA sequences. In the context of this study, PCR is employed to verify the presence or absence of plasmid DNA in transformed potato plants. By using specific primers for plasmid sequences, researchers can distinguish between plants that contain only the desired potato gene and those that also have plasmid DNA.