Discoveries made by DNA reached a phenomanol point in enabling the slightest of clues such as saliva on a cup to become a solid lead as all humans are of a different DNA code with the exclusion of monozygoyic twin. DNA profiling is 99.99 accurate or from a theoretical risk of a coincidental match 1 in 100 billion (100,000,000,000), although the practical risk is actually 1 in 1000 because monozygotic twins are 0.2% of the human population putting a higher risk of fail on DNA contamination then to have the same DNA.
Double Helix (AKA) "DNA"
Storing of DNA samples
 |
| DNA (deoxyribonucleic acid) |
1. Biological evidence should be allowed to air dry before packaging.
- ideally, it should be hung up in a clean dry room, away from direct sunlight
2. Biological evidence should be packaged in paper bags.- ideally, it should be hung up in a clean dry room, away from direct sunlight
- paper breaths, and allows the item of evidence to remain dry.
- Plastic bags do not breath, and can cause moisture and mold to grow on the evidence, which in turn can have a negative affect on DNA testing
3. Biological evidence should be stored under laboratory conditions as available resources permit
or in a cool, dry climate, free of moisture 4. Place liquid items in collection tubes and refrigerate
Methods of gathering DNA
| DNA Swab Kit |
1. Photograph stain/sample with and without a scale
2. Carefully swab the stain
- preferably with no dilution
- if stain is dry, use one drop of distilled water on the swab
3. Allow to air dry before packaging - preferably with no dilution
- if stain is dry, use one drop of distilled water on the swab
4. Carefully label & seal (date, time, initials).
5. Maintain the chain of custody.
6. Provide information that you think may be important.
- Note if items were collected from an unusual location or might have possible contaminants.
7. Forward to the forensic lab ASAP- Note if items were collected from an unusual location or might have possible contaminants.
Before a DNA test can be performed, a control sample should be
obtained from the victim, suspect, and any other persons whose DNA
may be found on the item of evidence.
Amongst a crime scene one of the things collected is DNA, but DNA is microscopic so how is it collected? DNA is collected by gathering substances that would contain DNA naturally or un-naturally such as blood stains, residue from a cigar, a water bottle, and much more obvious and some not so obvious sources. The process for collecting DNA is simple enough find a source but the caution needed is to the extreme; even the slightest patch of germ can cause cross-contamination to which will make evidence invalid. In order to prevent this precautions are taken such as wearing proper equipment such as glove, shoe wrappings, and baggies for containment.
Once in the back in the lab with the DNA samples then a standard order of events will taken to which vary on the type of analysis.
1 Briefing & signing of documents,
2 DNA extraction,
3 PCR amplification of selected Short Tandem Repeat (STR) markers(part may vary depending on type)
4 Automated DNA analysis
5 Statistical analyses of matching DNA profiles
6 Release of results to all parties concerned
Types of Analysis
Restriction Fragment Length Polymorphism (RFLP)
RFLP is a technique for analyzing the variable lengths of DNA fragments that result from digesting a DNA sample with a special kind of enzyme. This enzyme, a restriction endonuclease, cuts DNA at a specific sequence pattern know as a restriction endonuclease recognition site. The presence or absence of certain recognition sites in a DNA sample generates variable lengths of DNA fragments, which are separated using gel electrophoresis. They are then hybridized with DNA probes that bind to a complementary DNA sequence in the sample.
RFLP was one of the first applications of DNA analysis to forensic investigation. With the development of newer, more efficient DNA-analysis techniques, RFLP is not used as much as it once was because it requires relatively large amounts of DNA. In addition, samples degraded by environmental factors, such as dirt or mold, do not work well with RFLP.
PCR Analysis
Polymerase chain reaction (PCR) is used to make millions of exact copies of DNA from a biological sample. DNA amplification with PCR allows DNA analysis on biological samples as small as a few skin cells. With RFLP, DNA samples would have to be about the size of a quarter. The ability of PCR to amplify such tiny quantities of DNA enables even highly degraded samples to be analyzed. Great care, however, must be taken to prevent contamination with other biological materials during the identifying, collecting, and preserving of a sample.
STR Analysis
Short tandem repeat (STR) technology is used to evaluate specific regions (loci) within nuclear DNA. Variability in STR regions can be used to distinguish one DNA profile from another. The Federal Bureau of Investigation (FBI) uses a standard set of 13 specific STR regions for CODIS. CODIS is a software program that operates local, state, and national databases of DNA profiles from convicted offenders, unsolved crime scene evidence, and missing persons.
Mitochondrial DNA Analysis
Mitochondrial DNA analysis (mtDNA) can be used to examine the DNA from samples that cannot be analyzed by RFLP or STR. Nuclear DNA must be extracted from samples for use in RFLP, PCR, and STR; however, mtDNA analysis uses DNA extracted from another cellular organelle called a mitochondrion. While older biological samples that lack nucleated cellular material, such as hair, bones, and teeth, cannot be analyzed with STR and RFLP, they can be analyzed with mtDNA. In the investigation of cases that have gone unsolved for many years, mtDNA is extremely valuable.
All mothers have the same mitochondrial DNA as their offspring. This is because the mitochondria of each new embryo comes from the mother's egg cell. The father's sperm contributes only nuclear DNA. Comparing the mtDNA profile of unidentified remains with the profile of a potential maternal relative can be an important technique in missing-person investigations.
Y-Chromosome Analysis
The Y chromosome is passed directly from father to son, so analysis of genetic markers on the Y chromosome is especially useful for tracing relationships among males or for analyzing biological evidence involving multiple male contributors.
Uses in the Crime
DNA profiling proves its use when it comes to confirming and matching victims to murder weapons from little amounts of evidence such as a pool of blood to stains of blood on a knife. proving even more of its use on confirming who was present to the crime scene and who may have committed the crime with as little DNA possible such as saliva on a cup or a strand of hair that had fallen off once the sample have been collected and run CODIS and the sample then matches the suspect then it is almost 100% undeniable that they had been there at the time of the crime. However there has been a case in which the suspect had injected other beings (human/animal) blood into his own blood stream
in order to by pass DNA profiling.
Case Involving DNA Profiling
A young woman was murdered in Phoenix, Arizona, and a pager found at the scene of the crime led the police to a prime suspect. He admitted picking up the victim but claimed she had robbed him of his wallet and pager. The forensic squad examined the suspect's pickup truck and collected pods later identified as the fruits of the palo verde tree. One detective went back to the murder scene and found several Palo Verde trees, one of which showed damage that could have been caused by a vehicle. The detective's superior officer innocently suggested the possibility of linking the fruits and the tree by using DNA comparison, not realizing that this had never been done before. Several researchers were contacted before a geneticist at the University of Arizona in Tucson agreed to take on the case. Of course, it was crucial to establish evidence that would stand up in court on whether individual plants have unique patterns of DNA. A preliminary study on samples from different trees at the murder scene and elsewhere quickly established that each Palo Verde tree is unique in its DNA pattern. It was then a simple matter to link the pods from the suspect's truck to the damaged tree at the murder scene and obtain a conviction.
The sources used to obtain my information has been through various books from the library and teacher as well as some internet site
Urls
http://www.ornl.gov/sci/techresources/Human_Genome/elsi/forensics.shtml
http://www.dnaforensic.org/dna_typing/dnatyping_2.html
Books
Crime and detection
Crime for idiots
and random assortment from the library
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