Loading dye increases the density of DNA samples, allowing them to sink into gel wells, and gives color to visually track samples. Larger DNA fragments with more base pairs move slower and are located toward the top of the gel due to their lower mobility. A marker or ladder containing DNA fragments of known sizes is used to determine the size of unknown fragments in a sample.

1. Please answer the following:
Describe the two functions of loading dye. (4 points)
Where would the larger fragments, those with the greater number of base pairs, be located;
toward the top of the gel or the bottom? Why? (2 points)
What color is the positive pole on an electrophoresis chamber? (1 point)
Suppose you have 4 fragments of 500bp each. How many bands would appear on the gel? (1
points)
What is the purpose of using a marker or a ladder? What is the difference between the two? (4
points)
Solution
Describe the two functions of loading dye. (4 points)
Loading buffer increases the density of the sample hence allows the DNA sample to sink into the
wells of the gel
Loading buffer gives color to the DNA sample therefore allows us to visually track the DNA
sample as it runs through the gel.
Where would the larger fragments, those with the greater number of base pairs, be located;
toward the top of the gel or the bottom? Why? (2 points)
Larger fragments are heavy hence they have low mobility. They will be seen towards the top of
the gel.
What color is the positive pole on an electrophoresis chamber? (1 point)
Positive pole is colored red and the negative pole black
Suppose you have 4 fragments of 500bp each. How many bands would appear on the gel? (1
points)
We would see just a single band. Since all the four fragments are of equal size, they run together
in gel
What is the purpose of using a marker or a ladder? What is the difference between the two? (4
points)
DNA ladders are used in gel electrophoresis to determine the size and quantity of DNA
fragments. marker or a ladder-These two terms mean essentially the same thing.