Determining unknown fragment sizes using a graph of the log of distance
fragment migrated versus size of band in standard.
DNA samples move through the gel in a logarithmic fashion, relative to the # of
base pairs; eg. the larger the fragment, the slower it moves. Using semilogarithmic paper, you can plot the DNA ladder and then compare your unknown
sample to this.
1. DNA ladder: Measure, in centimeters, the distance the DNA ladder moved
in the gel (from the leading edge of the well to the leading edge of the
fragment image). Record this information
2. Unknown DNA fragments: Measure, in cm., the distance the restricted
DNA sample fragments moved in the gel. Record this information
Graphing to determine the length of fragments
1. Divide the horizontal axis into cm units. Between 1 - 7 cm.
2. Divide the logarithmic scale (vertical axis) into 100's, 1000's, and 10,000's, as
instructed.
3. Plot the data for the DNA ladder on the graph.
4. Connect, as best possible, the points with a straight line.
5. Plot the results of the restricted fragments on this graph. Do this by finding the
appropriate value on the graph (in cm.) for each DNA fragment. Once this value
is located, then move up to where this value intersects the plotted line for the
known DNA ladder.