Preparing the DNA for electrophoresis A dye is added to the sample of DNA prior to electrophoresis to increase the viscosity of the sample which will prevent it from floating out of the wells and so that the migration of the sample through the gel can be seen. The fragments in the marker are of a known length so can be used to help approximate the size of the fragments in the samples.
The prepared DNA samples are then pipetted into the remaining wells of the gel. When this is done the lid is placed on the electrophoresis tank making sure that the orientation of the gel and positive and negative electrodes is correct we want the DNA to migrate across the gel to the positive end. Separating the fragments The electrical current is then turned on so that the negatively charged DNA moves through the gel towards the positive side of the gel.
Shorter lengths of DNA move faster than longer lengths so move further in the time the current is run. The distance the DNA has migrated in the gel can be judged visually by monitoring the migration of the loading buffer dye. The electrical current is left on long enough to ensure that the DNA fragments move far enough across the gel to separate them, but not so long that they run off the end of the gel.
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Thankyou, we value your feedback! We use cookies to improve this site. Because each DNA molecule is negatively charged, it can be pulled through the gel by an electric field. The bands furthest from the start of the gel contain the smallest fragments of DNA. The bands closest to the start of the gel contain the largest DNA fragments. Gel electrophoresis can be used for a range of purposes, for example:.
However, gel electrophoresis can also be used to separate out proteins. Different proteins have different sizes, mainly due to the number of amino acid building blocks in their structure.
Chemical modifications attached to the protein also affect its size. Different proteins also have different charges. This can result from both the types of amino acid used to construct them, as well as the types of modifications attached to them. Different types of electrophoresis gels are used to provide different types of information. The type of gel you choose therefore depends on the type of question you are asking. Typically, gels made from polyacrylamide are used to separate proteins on the basis their different sizes.
Usually, the proteins are first treated with heat and a chemical called SDS in order to unravel the protein. Compare the bands in each sample and determine if either suspect left the blood found at the crime scene. What do you notice when you compare the patterns? Although one band is common in each of the three examples see the arrow , remember that all bands must align for two samples to be considered a match.
Therefore, since all the bands in suspect 2 match with all the band of the blood sample, we can conclude that the blood sample had to have come from suspect 2. Another use of DNA fingerprinting is in paternity cases. Since a child receives half of his or her DNA from the mother and the other half from the father, paternity can be established. A DNA fingerprint is obtained from the mother, the child, and the alleged father. These fingerprints are compared with each other.
Every band that appears in the child's fingerprint must come from either the mother or the father. If there is a band in the child's fingerprint that does not appear in the mother's or the alleged father's fingerprint, then the alleged father could not be that child's father. You may be familiar with these uses of DNA fingerprinting. There is another common and valuable use of this technology, and this involves diagnosis of diseases. If a genetic disease runs in a particular family, the DNA from each member of the family can be analyzed and a pattern may emerge.
For example, if every individual in a family that is affected by a disease has a DNA band at one site in the gel, and individuals who are not affected do not have this band, then that band can be said to be linked to the disease. It can be used as a marker to indicate who has, or who will develop the disease. This marker can also be used to determine if unborn children will develop the disease.
You will find two examples of the use of DNA fingerprinting. Take a look at them. One asks you to determine if you can clear up a paternity case, and the other requires you to find a marker for a particular genetic disease.
Good luck with your investigations!! Jennifer and Steven Barker had been married for five years. They had a good relationship but they began to drift apart. They decided to get a divorce. Everything was relatively civil, and the assets from the marriage were divided equally between the two. However, there was a disagreement about the car -- a Mercedes Benz purchased after the wedding with joint funds.
Both Jennifer and Steven loved the car and neither would give it up. The judge in the case, Judge Tomson, decided Steven would get the car. Several months after the break up, Jennifer discovered she was pregnant.
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