1. Why Do Cheek Cells Make A Convenient Source For Obtaining DNA Samples?

In this laboratory, two experiments were performed; the first one was performed to determine whose fingerprint was found at a crime scene. For this experiment, four-10 mL DNA samples were placed in a well of agarose gel, using a micropipette; the sample was also covered in a TBE buffer solution. The four samples were then put in the electrophoresis apparatus to be run through electrophoresis. After 20 minutes, the samples were ready and the results were documented; it was found that suspect “B” was the culprit.
The second experiment was performed to isolate and extract DNA from epithelial cells. 1 mL of 8% sodium chloride solution was put into a test tube. 10 mL of tap water was put into a cup and one individual from each lab group put
The first question was “Why do cheek cells make a convenient source for obtaining DNA samples?”. Cheek cells are composed of epithelial cells, which are those cells that “cover the internal and external surfaces of the body and line hollow structures,”(Facts On File). These cells are flat and cover the surface of the inner cheek. This is suitable for harvesting DNA because of the presence of the Barr body, “A condensed clump of chromatin (DNA) which corresponds to an inactivated X chromosome,” (Facts On File). The Barr body is only found in females, so when extracting DNA from cheek cells to determine sex, the DNA will match a female if the Barr body is found. The only way that a male could have a Barr body is if a genetic mutation occurred; in that case, the extraction of DNA from cheek cells would be
When the DNA was released from the cheek cells, 1 mL of 10% sodium lauryl sulfate was added to the test tube. Sodium lauryl sulfate works as a detergent that removes the cheek cell from its cell membrane, allowing the DNA to be released into the test tube. After the DNA was released into the test tube, 5 mL of 95% cold ethyl alcohol was added so it formed a layer over the cheek cells and so it could start precipitation. Any clouding that formed between the cheek cells and ethyl alcohol was a polymer of DNA; this clouding occurred because DNA is insoluble in alcohol. DNA can then be “spooled” onto the glass rod because the polymers of DNA are now visible. Therefore the DNA precipitates where the cheek cells and ethyl alcohol