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 context of the problem. The researchers are using recombinant DNA technology to transfer a blight resistance gene from a resistant potato variety into a susceptible variety. They aim to identify plants that contain only the potato gene and are free of plasmid DNA sequences using PCR analysis.
2. Step 2: Review the role of PCR (Polymerase Chain Reaction) in this experiment. PCR amplifies specific DNA sequences using primers that bind to target regions. In this case, primers specific to plasmid DNA are used to detect the presence of plasmid sequences in the transformed plants.
3. Step 3: Analyze the gel electrophoresis results. Gel electrophoresis separates DNA fragments based on size, and the presence of bands indicates successful amplification. The positive control lane shows amplification of plasmid DNA, confirming the primers work. The negative control lane shows no amplification, confirming the absence of contamination.
4. Step 4: Compare the lanes corresponding to the transformed plants with the control lanes. Plants containing only the potato gene will show no bands in the PCR lane because the primers specific to plasmid DNA will not amplify any sequences. Plants with plasmid DNA will show bands, indicating the presence of plasmid sequences.
5. Step 5: Conclude which plants contain only the potato gene based on the absence of bands in their respective PCR lanes. This indicates that these plants are free of plasmid DNA and contain only the desired potato blight resistance gene.

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 recent study avoided plasmid genes, focusing solely on the potato gene to enhance the specificity of the transformation.

Polymerase Chain Reaction (PCR)

Polymerase Chain Reaction (PCR) is a molecular biology technique used to amplify specific DNA sequences, allowing for the detection of particular genes. In the context of the study, PCR was employed to identify which transformed potato plants contained only the resistance gene without any plasmid DNA. The results from gel analysis of PCR products help determine the success of the gene transfer and the purity of the transformed plants.