Gel electrophoresis is a procedure utilized in biochemistry and molecular biology (also used in situations such as crimes scenes and DNA testing) to separate DNA molecules by size. In order to perform gel electrophoresis, DNA (which is negatively charged due to the phosphate groups in the backbone of DNA) and thus DNA will travel towards the positive electrode. During this procedure it is evident that as the pieces of DNA travel through the gel they will meet a resistance, meaning that it would be more difficult for larger pieces of DNA to move through the gel than smaller fragments, thus larger fragments move slower than smaller fragments. This is what allows the separation of all different sizes of DNA fragments.
State that gel electrophoresis DNA is used in DNA profiling:
In a crime scene for example, Investigators might find signs of the suspects DNA. However, a test tube full of DNA all looks the same, so it is not possible to tell the DNA coding by just looking at it. Gel electrophoresis is a technique scientists utilize to find out exactly what DNA they have in order to determine whether it relates to the suspects DNA or not. This technique is done by separating DNA molecules by size.
Describe the application of DNA profiling to determine paternity and also in forensic investigations:
Each individual (excluding identical twins) carries a distinct DNA genome made up of nucleotides. In a paternity test, a sample of cheek cells, for example can be collected as it contains a blueprint of this genetic code, inherited from both the mother and the father. In a paternity test, a DNA sample is taken from the child, along with its mother and its believed to be father and the analysis begins by exposing the samples to various restriction enzymes in order to cut up the DNA and place it in a gel matrix. The gel matrix is then placed in an electrophoresis chamber containing positive and negative electrodes as current runs through the chamber. Due to the fact that DNA is negatively charged it travels towards the positive pole. As time passes the larger fragments will move slowly as smaller fragments. Think of it as a partially permeable membrane where smaller cells have the ability to diffuse through the membrane as larger cells are prevented due to their surface area to volume ratio. At the end of the test the results are compared. Due to the fact that half the genetic material is from its mother, half of the pattern will be similar to the child’s. If the father is the child’s biological father then the rest of the pattern will be similar as well.
In a forensic investigation the same method is carried out. However instead of gathering DNA samples from parents and children, they gather DNA from suspects. For example in the case of rape there might be remaining sperm cells around the victims vagina. This can be collected, analysed and used against the suspect.
