ONE PICTURE'S WORTH A THOUSAND WORDS
DNA fingerprinting is used routinely today in criminal cases. The process involves analyzing the suspect's DNA and comparing it to the DNA of the criminal from a sample left at the crime scene. The analysis requires the DNA to be cut up with restriction enzymes and then analyzed by agarose gel electrophoresis, which separates DNA pieces based on size. The DNA appears as bands on the gel. The sample from an individual looks similar to the bar codes supermarkets use to scan for prices. Since no two people have the same DNA, the pattern will be unique for each individual. If the pattern of the accused matches the pattern from the sample left at the scene of the crime, then the sample must belong to the suspect.
Consider the following example. Two robbers broke into an electronics shop late one night and stole equipment and cash. They were careful to wear gloves and not leave any traditional fingerprints. However, one of them was cut when climbing through the broken window, and a small sample of blood was left behind. Several days later, the police picked up two men selling stolen electronic equipment and believed them to be the ones who robbed the shop. Samples of blood were taken from each suspect and the DNA was isolated. Genetic material was also isolated from the blood sample left at the crime scene. Each DNA sample was cut up with restriction enzymes and subjected to gel electrophoresis. The resulting gel is shown below. B is from the blood sample found at the crime scene, S1 is the DNA from the first suspect, S2 is the DNA from the second suspect. The lines (or bands) represent pieces of DNA of different sizes. If two samples come from the same individual, all bands in one sample must match up with all the bands in the other. 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!!
ROCK A BYE BABY
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. She claimed Steven was the father and demanded he pay child support. Steven denied he was the father. He claimed Jennifer was just trying to get back at him for keeping the car and refused to pay any support for her baby. The legal battle went on for months, until well after baby Andrew was born. As with the dispute over the car, Judge Tomson again had to settle the case. She ordered DNA fingerprinting done on Jennifer, Steven, and Andrew.
Take a look at the DNA fingerprint analysis.
Remember, to conclude that the alleged father is truly the father, every band in the
child's fingerprint that does not match in the mother's fingerprint must match in the
- M is the mother, Jennifer Barker.
- C is the child, Andrew Barker.
- AF is the alleged father, Steven Barker.
Is Steven Barker the father or not?
A FAMILY DISEASE
The Rieser family had a long history of a strange disease. The earliest known case of the disease occurred in Jeb Rieser back in 1765. Originally from a small village in England, he was the first member of the family to come to America. When he was about thirty-five years old, Jeb developed problems walking and coordinating his fine motor movements. He deteriorated rapidly, loosing all muscle movement, and died several years later. He left his widow with five children, none of whom developed the disease.
As the years passed and the family grew larger, many other cases of this strange disease were noted. In 1896, a doctor diagnosed the disease as Jenkins neuromuscular disorder (JND), naming the disease after himself for having discovered it. Dr. Jenkins had no cure and no treatment for the family but he did recommend that no member of the family have children until they were over thirty-five years old to ensure the disease would not spread. Few followed his advice. Most of the Riesers were farmers and needed help with the land. Large families were needed. They could not wait until late in life to have children.
One day in 1989, a descendent of old Jeb, Alex Rieser, was watching TV and heard a news report. It seems that doctors could now do a DNA test to determine if someone could inherit a disease called Huntington disease, which was very similar to JND. Alex was twenty-nine years old and recently married. He very much wanted to start a family but did not want to take a chance of passing on the deadly disease. Alex decided to contact a genetic counselor at the local hospital. The counselor told him there was a chance the disease could be diagnosed with a genetic test. The test would require DNA fingerprints from individuals in the family who had the disease and individuals who were over thirty-five and didn't have the disease. Alex's relatives decided to help.
Below is a picture of DNA fingerprints of eight members of the Rieser family. Individuals 4, 6, and 8 have JND. The other family members do not have the disease. Is there a particular fragment of DNA that is associated with individuals who have the disease? If so, which one is it? Could you determine if Alex Rieser will develop this disease? How?
As it turns out, Jeb Rieser had several brothers and sisters back in England. Some of their descendants also developed this strange disease. Could this test be used to determine if a member of the English side of the family will come down with JND?