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.

Video transcript

Welcome back. Here's our next question. The technique to separate DNA fragments on the basis of their size or density on a gel using electric current is referred to as. And our choice is our choice a preliminary chain reaction choice B recombinant DNA technology. Choice C gel electrophoresis or choice D. D. N. A. Sequencing. Well this process is choice C gel electrophoresis. Um The word gel and then electro the prefix there might help us zoom in on this if we couldn't recall. Um This is because D. N. A. Has a negative charge. So if you put A D. N. A sample loaded in a little well on a gel here and apply an electric current, the negatively charged D. N. A. Is going to migrate in the direction of that positive terminal. And the smaller fragments as these fragments move through the gel, they're going to encounter friction from the gel molecules. And that will mean that larger DNA fragments are not going to go as far and the smaller the fragment the further it will go. You'll end up with a pattern, something like that with your fragments separated by size. Um Let's just look at our other answers to see why they're not correct. Choice. A preliminary chain reaction. Um That's used to make identical copies of a short sequence of D. N. A. So that's not what we're looking for. Choice B recombinant DNA technology. The recumbent there indicates we take a gene of interest that codes for a protein we might want to study and actually splice it into the genome of a bacterial cell or a yeast cell and then use that cell is like a little factory to either study the gene or turn out copies of the protein. Um So that's not what we're talking about here. And finally, Choice D. D. N. A. Sequencing. DNA sequencing does utilize gel electrophoresis. Um But it's a very specific technique used to find the sequence of bases in a given D. N. A. Segment. So that's not what we're describing here. So the technique to separate those DNA fragments on the basis of their size on a gel using electric current. Electric current is choice C gel electrophoresis. See you in the next video.