In this section of the lab the agarose gel was ran with a 200 bp ladder as a reference in order to determine the size of the fragments for the investigators DNA. The 200 bp ladder DNA fragments and size can be seen in table 2.
Table 2. The distance migrated by the fragments in the 200bp ladder. The piece of DNA that migrated the furthest was automatically described as 200 base pairs. Each band previous was increased 200 base pairs. The data obtained was used to make a plot of the ladder DNA that corresponds to the distance traveled on 3% agarose.
Distance Migrated (mm) |
Base pairs |
16.5 |
1200 |
26.0 |
1000 |
32.0 |
800 |
45.0 |
600 |
50.5 |
400 |
65.5 |
200 |
Figure 4. The plot of the ladder displaying base pairs that correspond to the distance traveled on the 3% agarose gel by the 200bp ladder. The y-axis was logged to produce a straight line and the exponential equation was used to calculate the corresponding base pairs for the bands. The equation displayed on the graph was used to calculate the base pairs of the crime scene DNA.
Table 3. The distance traveled by the bands of the crime scene DNA observed on a 3% agarose gel. The allele size was calculated using the equation y=2498e^-0.036x, where x represents the distance travelled. The number of repeats were determined using the allele sizes and frequencies at the D1S80 locus provided by Kluftinger and Plunkett (2015).
Distance Traveled (mm) |
Allele size (bp) |
Number of Repeats |
Allele Frequency |
46 |
476 |
20 |
0.0210 |
49.5 |
420 |
17 |
0.0143 |
62 |
268 |
- |
- |
The lab VNTR results didn't appear for the investigators, the gel that lacks DNA can be seen in the experimental gels section. Some of the reasons that there was no DNA on the agarose gel could have been because the cheek was not chewed well enough. There could have been a chelex bead left in solution which would inhibit PCR. This could happen because they chelex beads can easily chelate the Mg that is required by the Taq DNA polymerase as a cofactor for catalysis. Any carryover of the chelex to the PCR reaction will prevent any PCR results from being present.