Use of Gel Electrophoresis, Lab Report Example

Introduction

Gel electrophoresis is used to separate DNA on the basis of its size. Due to the differential charge between the negative end of the gel bath and the positive end of the gel bath, the negatively charge DNA is separated on the basis of charge; smaller pieces of the negative charged DNA move more quickly though the pores of the gel and appear closer to the bottom of the gel, while larger pieces of the positively charged DNA move more slowly through the pores of the gel and remain closer to the top of the gel. Thus, gel electrophoresis can be performed to determine the identify of DNA based on size and identity. This is a commonly used application in crime scene investigation to determine the DNA matches between suspects and evidence.

Materials and Procedures

The agarose gel was prepared in the casting tray. After the comb was removed, the agarose gel was submerged in buffer. Each sample dye was then loaded into consecutive wells. The safety cover was then connected, and the leads were connected to the power source to begin electrophoresis. The first two wells were made to contain crime scene DNA (A and B), while the second two wells contained DNA from the first suspect (C and D), and the final two wells contained DNA from the second suspect (E and F).

Results

Figure 1 shows what the DNA in the electrophoresis bath looked like before the power source was applied. Figure 2 shows an idealized sample of what the results should have yielded. These figures show that the DNA is made up of several different sections of DNA that could be used to characterize the DNA sequence of the criminals at the crime scene. The DNA at crime scene 1 (lane A) is a perfect match for suspect 1 DNA 1 (lane 3) and suspect 2 DNA 1 (lane E). Meanwhile, the DNA at crime scene 2 (lane B) is a perfect match for suspect 2 DNA 2 (lane F). Thus, it could be said that both of the suspects were involved with the first crime, while only suspect 2 was involved with the crime that occurred at the second crime scene.

Discussion

This experiment demonstrated that it is plausible to use gel electrophoresis to differentiate the DNA of different individuals. Restriction enzymes digest these molecules differently based on the base pair sequence, yielding DNA that is of different sizes. Thus, DNA of suspects can be compared to the DNA that is found at crime scenes to determine whether the suspect was present at the crime scene. In doing so, it is possible to use scientific evidence to confirm or deny an individual’s guilt.

Possible errors that frequently occur with DNA electrophoresis is allowing the gel to run for too long, which will allow the stained DNA fragments to go beyond the gel. Furthermore, if the DNA is inserted into the gel incorrectly, there can be potential cross contamination between samples, which would interfere with the generation of effective results. A final mistake that could be made is reversing the flow of electricity so that the DNA flows in the wrong direction. In spite of these potential errors, DNA electrophoresis remains an effective tool for comparing and contrasting DNA. Furthermore, these errors can be avoided if the DNA is multiplied using PCR so there is additional sample available in case of error.

Conclusion

It was found that suspects 1 and 2 were involved in the crime at crime scene 1, while only suspect 2 was involved with the crime that occurred at the second crime scene. The ability to use DNA evidence to determine the identity of criminals is a pertinent tool for use in forensic science.