DNA Fingerprinting: Applications & Famous Cases PDF

Its Application in the Justice System and Biomedical Doubts Prepared By: Marjun P. Goron What is DNA Fingerprinting? A technique used by scientists to distinguish between individuals of the same species using only samples of their DNA a.k.a. DNA Profiling  Who Invented it? The...

Its Application in the Justice System and Biomedical Doubts Prepared By: Marjun P. Goron What is DNA Fingerprinting? A technique used by scientists to distinguish between individuals of the same species using only samples of their DNA a.k.a. DNA Profiling  Who Invented it? The process of DNA fingerprinting was invented by Alec Jeffreys at the University of Leicester in 1985.  A DNA Fingerprint When many genes are analyzed, each with many different alleles, the chance that two patterns match by coincidence is vanishingly small.  Stages of DNA Profiling Stage 1 Cells are broken down to release DNA If only a small amount of DNA is available it can be amplified using the polymerase chain reaction (PCR) Stages of DNA Profiling Step 2 The DNA is cut into fragments using restriction enzymes. Each restriction enzyme cuts DNA at a specific base sequence. Stages of DNA Profiling The sections of DNA that are cut out are called restriction fragments. This yields thousands of restriction fragments of all different sizes because the base sequences being cut may be far apart (long fragment) or close together (short fragment).  Stages of DNA Profiling Stage 3 Fragments are separated on the basis of size using a process called gel electrophoresis. DNA fragments are injected into wells and an electric current is applied along the gel. Stages of DNA Profiling  DNA is negatively charged so it is attracted to the positive end of the gel. The shorter DNA fragments move faster than the longer fragments. DNA is separated on basis of size.  The DNA Fragments Are Separated on the Basis of Size The technique is gel electrophoresis. The pattern of DNA bands is compared between each sample loaded on the gel. Stages of DNA Profiling A radioactive material is added which combines with the DNA fragments to produce a fluorescent image. A photographic copy of the DNA bands is obtained. Stages of DNA Profiling Stage 4 The pattern of fragment distributio n is then analysed. Biological materials used for DNA profiling Blood Semen Saliva Hair Body tissue cells DNA samples have been obtained from vaginal cells transferred to the outside of a condom during sexual intercourse. Uses of DNA Profiling DNA profiling is used to solve: Crimes; and medical problems Crime Analysis Forensic science is the use of scientific knowledge in legal situations. The DNA profile of each individual is highly specific. The chances of two people having exactly the same DNA profile is 30,000 million to 1 (except for identical twins). DNA Profiling can solve crimes The pattern of the DNA profile is then compared with those of the victim and the suspect. If the profile matches the suspect it provides strong evidence that the suspect was present at the crime scene (BUT….it does not prove a person committed the crime). If the profile doesn’t match the suspect then that suspect may be eliminated from the enquiry. Exampl e A violent murder occurred. The forensics team retrieved a blood sample from the crime scene. They prepared DNA profiles of the blood sample, the victim and a suspect as follows: Was the suspect at the crime scene? Suspects Blood Victims Profile sample from profile crime scene  DNA, the Law, and Many Other Applications – The Technology of DNA Fingerprinting The defendant stated that the blood on his clothing was his. A DNA fingerprint used in a murder case. Famous Cases Colin Pitchfork was the first criminal caught based on DNA fingerprinting evidence. He was arrested in 1986 for the rape and murder of two girls and was sentenced in 1988. Solving Medical Problems DNA profiles can be used to determine whether a particular person is the parent of a child A child's paternity (father) and maternity (mother) can be determined This information can be used in Paternity cases Inheritance cases Example: A Paternity Test By comparing the DNA profile of a mother and her child it is possible to identify DNA fragments in the child which are absent from the mother and must therefore have been inherited from the biological father. Is this man the father of the child? Mother Child Man Famous cases In 2002 Elizabeth Hurley used DNA profiling to prove that Steve Bing was the father of her child Damien DNA, Medicine and the Law Some applications of DNA fingerprinting in the justice system and bio-medical doubts. SLT 3/8/05