Besides using electrophoresis to separate DNA fragments according to their sizes, it can be used to estimate the actual size, in base pairs, of each fragment. For example, we might be looking for a gene and we suspect it is of a certain size; electrophoresis can be used to locate fragments in that size range. In order to do this, we would need to run a gel with a mixture of DNA fragments of known sizes. This mixture called a "marker" or "ladder," serves as a control or a standard to which we can compare the positions of other DNA bands in the same gel.
In the diagram, below, the "marker" lane contains 10 DNA bands of known sizes. These sizes are given below. Using this information and the plasmid maps of pARA and pKAN-R, predict the positions of DNA bands produced the pARA -, pARA +, pKAN-R-, pKAN-R + samples. Hint: first determine how many fragments should appear in each sample, and then determine the size(s) of each fragment. We will omit the "LIG" sample.