Gel Electrophoresis

Dna fingerprinting in criminal justice system

DNA fingerprinting was developed in 1984 by Alec. J. Jeffrey. The structure of DNA (deoxyribose nucleic acid) was first discovered by Dr James Watson and Francis Crick in 1953. DNA fingerprinting is a form of identification based on sequencing specific non-coding portions of DNA that are known to have a high degree of variability from person to person.  These sections are known as Tandem repeats. The discovery of DNA fingerprinting revolutionized criminal identification and forensic science. DNA is a chemical structure that forms the genes. DNA fingerprints are unique to every individual and can be used as legal evidence in court to prosecute or defend alleged criminals. And also in paternity cases, DNA fingerprinting technology can be used to identify or rule out persons as biological parents of a child. The DNA fingerprinting process is called gel electrophoresis. It is a process that can sort pieces of DNA according to its size. One country that has very successfully implemented a national DNA database is Britain.

 

 

HOW DOES DNA WORKS?

1. VNTR's (variable number of Tandem repeats) can be recognized as the variable numbers of repeated nucleotides can be found in DNA and can be used for identification of individuals. the repeat number may vary from one to thirty repeats, these repeat regions are usually bounded by specific restriction enzyme sites. This is something which a child gets from both of his parents.

 

1. Classes of satellite DNA called Short Tandem Repeats (STR) stretches of DNA containing tandemlyrepeated nucleotide sequences in which the repeat unit is at least two bases but no more than seven in length. A specific STR is characterized by the sequence of its repeat unit and the number of times that unit is repeated.

 

 

 

STAGES OF DNA FINGERPRINTING-

1. Cells are broken down to release DNA. If only a small amount of DNA is available it can be amplified using polymerase chain reaction (PCR).
2. The DNA is cut into fragments using restriction enzymes. Each restriction enzyme cuts DNA at a specific base sequence. 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).
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. 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 the basis of size. A radioactive is added which combines with the DNA fragments to produce a fluorescent image. A photographic copy of the DNA bands is obtained
4. The pattern of fragment distribution is then analyzed.

 

BIOLOGICALLY USED DNA FINGERPRINTING

 

• Blood
• Hair
• Saliva
• Semen
• Body tissue cells
• DNA samples have been obtained from vaginal cells transferred to the outside of the condom during sexual intercourse.

 

APPLICATION OF DNA FINGERPRINTING

• Diagnosis of inherited disorders such as haemophilia, cystic fibrosis etc.
• Developing cures for inherited disorders.
• Forensic or criminal use and determination of paternity cases.
• Personal identification.

 

EXAMPLE

Blood found at the scene of a crime contains white blood cells that contain DNA. Forensic scientists can then take a sample of the blood, isolate the unique section of DNA and perform electrolysis to make a DNA fingerprint. All tried and convicted criminals have their DNA fingerprints in a database so they can be easily identified if they re-offend.

 

DNA IN CASE OF PATERNITY

DNA fingerprinting can also be used to resolve paternity disputes. DNA samples are taken from the mother, child, and alleged fathers, and electrophoresis is used to create DNA fingerprints of all the samples. When the DNA fingerprints are compared, all the nodes in the child‟s DNA fingerprint must match up with nodes from either the mother or the father. The child cannot have a single node that has not come from either the mother or father. Using this method, potential fathers can be eliminated.

 

ADVANTAGES OF DNA FINGERPRINTING

DNA fingerprinting has contributed heavily to the development of several industries concerning health and forensics. People sometimes worry about what could happen to their genetic information if it were to fall in the wrong hands. The most important advantage of DNA fingerprinting is that there is strong similarities shown between genetic fingerprints of parents and children. This is a benefit because a child's genetic fingerprint is made up of half the father's genetic information and half of the mother's information. This means that the bands of a child's genetic fingerprint will match the bands on both of their parents, making it possible to establish paternity and maternity tests.Laws and regulations have to be made in order to control the lawful and constructive use of such technologies, and individuals have to decide how willing they are to supply their DNA information for national registers and testing. over the past two decades at least, DNA fingerprinting has enabled more genes to be identified and more criminals to be convicted than ever before, making it one of the most revolutionary discoveries of science yet.

 

DISADVANTAGES OF DNA FINGERPRINTING

A particularly famous case in which the use of DNA fingerprint evidence was questioned by the court was that of O.J. Simpson, 1994-1995, who allegedly murdered his ex-wife her friend. Simpson‟s defence attorneys argued that the way in which the DNA samples were collected did not meet forensic standards, hence jeopardizing the DNA evidence. Because of the discrepancies over the collection methods of the DNA evidence presented in his case, Simpson was not charged with murder. The development of this technology has given rise to a number of ethical debates including whether a person can be forced to give a DNA sample for analysis and who should gain access to such personal information. Also, the concept of a DNA database raises questions about personal privacy and civil rights, although it could be a key contributor to genetic research. Scientists are consistently finding new ways in which the applications of DNA can be expanded. One of the main problems with the process of DNA fingerprinting is that the sample can be easily ruined. The tiniest pieces of genetic junk can contaminate DNA samples, causing them to be useless. Another limitation of fingerprinting is that the procedure is so complex and hard to read the DNA patterns, that sometimes the juror finds the evidence almost invisible.

 

 

CASE REFERENCES

1. Desmond Applebee- First case of DNA evidence in Australian criminal proceedings. The accused was charged of sexual assault and initially denied any contact, but altered his defense to consensual intercourse after DNA  evidence was admitted a part of Crown case. He was convicted by the jury.

 

1. R V. Tran (1990 50 A Crim R 233) - Conflicting expert evidence on DNA test results held inadmissible due to tendency to produce a misleading and confusing impression for the jury.

 

 

1. R v. Lucas (1992 2 VR 109) - DNA evidence tendered to establish source of a bloodstain on a wall by reference to DNA samples was held inadmissible  due to its probative value being outweighed by its possible prejudicial effect.

 

1. R v Jarrett (1994 62 SASR 443) - Laboratory process of constructing DNA profiles using PCR techniques judicially considered and accepted. The question whether forensic experts had performed analysis competently was held to be a matter for the jury to decide.

 

 

1. R v Karger (2001 SASC 64)-  Murder trial involving a three-month preliminary hearing to review the scientific acceptability of the Profiler Plus system. The DNA evidence was admitted.

 

About the Author

Important Information About DNA Paternity Testing

DNA Paternity Testing is amongst the current breakthroughs in science and technology.  It's has been useful in several situations like getting rid of family issues and helping in law enforcement matters.  In contrast to in the olden days, DNA Testing is now more obtainable and reasonably priced.

There are numerous techniques in administering Paternity DNA Test yet the widely used strategies in the world today are Polymer Chain Reaction Method (PCR) and Restriction Fragment Length Polymorphism (RFLP).  The PCR Method is utilizing polymer - a large molecule made up of repeating structural units.  In this process, DNA is extracted, fragmented, amplified and then separated by the process of gel electrophoresis.  The sequence of the DNA fragments will be studied and compared.

In the mean time, Restriction Fragment Length Polymorphism (RFLP) utilizes the homologous DNA sequences.  In this type of DNA Test, the taken out DNA is fragmented by enzymes.  The DNA fragments are then categorized by size and then undergo identification.

In both methods, DNA samples from the father and the mother is compared with the offspring’s DNA.  DNA Paternity Test can carry on even without DNA samples from the mother however it will take a bit more of laboratory work.  Every single band of the offspring’s DNA must match a band with the father to summarize that she or he indeed his child.

In Prenatal Paternity Testing, samples of the unborn baby’s DNA are acquired by means of the Chorionic Villi Sampling (CVS) procedure or the Amniocentesis Procedure.  In the 1st procedure, placenta cells are collected while in the 2nd procedure, fetal cells from the amniotic fluid are collected.  Each of these testing methods are invasive procedures and could have certain amount of risk hence it should not be performed with no advice of an OB-Gyne.

On the other hand, ethical and health concerns surround prenatal paternity testing because of the possible risks to the fetus.  It is as a result suggested that DNA Paternity Testing be done right after the child is born.  It's less dangerous and a lot more affordable that way.  It can be carried out simply by taking blood sample in the umbilical cord.

For Home DNA Paternity Test, huge difference is that samples are accumulated in your home.  Procedure resembles a traditional DNA paternity test and is just as precise.  For this process, the samples are sent in to a testing company laboratory.  People generally make use of this method for personal purposes only like mere attention and to reconcile their doubts.  Be reminded that in this kind of procedure, the actual result is not admissible in court.  As a result if you're planning to provide the exact result in court, home DNA paternity testing isn't the suitable method.

Is Southern blotting a type of gel electrophoresis?

I understand the entire point of gel electrophoresis, but I don't know if Southern blotting is a type of gel electrophoresis. Is it?

It is an electrophoretic technique, but not a separation technique, and it is not strictly a gel technique because the material is removed from the gel. The suffix -phorēsis is from the Greek for "to carry" or "to bear". In the blotting technique, the separated material on the gel is transfered to filter paper, so an electrical field moves the material from one medium (the gel) to another (the filter paper).

Retrospective study of necrotizing fasciitis and characterization of its associated Methicillin-resistant Staphylococcus aureus in Taiwan (biomedcentral)

Background: Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as
a prevalent pathogen of necrotizing fasciitis (NF) in Taiwan. A four-year NF
cases and clinical and genetic differences between hospital acquired (HA)- and
community-acquired (CA)-MRSA infection and isolates were investigated.
Methods: A retrospective study of 247 NF cases in 2005-2008 and antimicrobial
susceptibilities, staphylococcal chromosomal cassette mec (SCCmec) types,
pulsed field gel electrophoresis (PFGE) patterns, virulence factors, and
multilocus sequence typing (MLST) of 16 NF-associated MRSA in 2008 were also
evaluated. Results: In 247 cases, 42 microbial species were identified. S.
aureus was the major prevalent pathogen and MRSA accounted for 19.8% of NF
cases. Most patients had many coexisting medical conditions, including
diabetes mellitus, followed by hypertension, chronic azotemia and chronic
hepatic disease in order of decreasing prevalence. Patients with MRSA
infection tended to have more severe clinical outcomes in terms of amputation
rate (p0.05) and reconstruction rate (p=0.001) than those with methicillin-
sensitive S. aureus or non-S. aureus infection. NF patients infected by HA-
MRSA had a significantly higher amputation rate, comorbidity, C-reactive
protein level, and involvement of lower extremity than those infected by CA-
MRSA. In addition to over 90% of MRSA resistant to erythromycin and
clindamycin, HA-MRSA ...

biomedcentral

Gel electrophoresis