Forensic Biology, the Toxicology Laboratory, Firearms and Toolmarks, the Medical examiner and CSI ethics.

Forensics

In this report, I will tell you about Forensic Biology, the Toxicology Laboratory, Firearms and Toolmarks, the Medical examiner and CSI ethics. Then, I will tell which job is the most and least interesting for me and why.

Forensic Biology

First, we learn about DNA. All biological samples contain deoxyribonucleic acid (DNA). DNA is a “blueprint” for making an entire person. It contains all the information that makes us unique individuals. Biological samples like blood, bones, hair, saliva, and skin cells all contain DNA. The nucleus contains most of the DNA. With the exception of identical twins, different people do not have the same DNA. Identical twins are when one egg cell is fertilized, then it’s divided to produce two identical cells (with identical DNA). DNA is the same throughout one person’s body. Because DNA is unique for each person (except identical twins) forensic scientists can use it to connect a suspect to a crime or to rule out a suspect in a crime.

A DNA profile is a summary of one’s person genetic information. The FBI manages the United States’ largest database of DNA profiles, called CODIS (Combined DNA Index System). CODIS contains DNA profiles from criminals, evidence collected at crime scenes, missing people, etc. Each person has two copies of each DNA marker: one inherited from each of his or her parents. These markers can be different lengths or they can both be the same length. Forensic DNA analysts use DNA profiles to compare DNA samples because every person’s DNA contains a huge amount of information. Labs all over the country use the same 13 markers to make DNA profiles.

Processing DNA is one of the most important things in a DNA lab. First, we have to collect a DNA sample, for example with a buccal swab. We use a buccal swab because collecting check cells is fast, easy, and painless. The DNA is inside the cellular and nuclear membranes. To extract it, we have to lyse, or burst, the cells and nuclei. The lysis solution causes the cell and nuclei to break apart and release the DNA. A technique called PCR (Polymerase Chain Reaction) allows us to copy the DNA markers millions of times, this step is called “amplify”. We need many copies of the DNA markers because DNA markers are very small, so having many copies makes them easier to find and analyze. The PCR reaction amplifies only the DNA markers. Once all the markers are amplified, they need to be sorted by size. Separating the DNA allows u to determine which lengths of markers are present in our sample. For that we need to move our sample to the Genetic Analyzer. The Genetic analyzer pushes the DNA through a very small tube filled with a gel-like material. Small fragments of DNA move through this gel faster than large pieces. A laser scans each group of copied DNA markers as it exits the tube. A sensor records the time the markers exit and sends this information to a computer. The last step is to analyze. A computer shows us the data from the Genetic Analyzer. A peak is formed each time a group of DNA fragments exits the gel and is scanned by the laser. The peaks of small pieces of DNA will appear first on the graph. The computer first separates the DNA sample by marker. All forensic scientists need to have their DNA profiles on record before they can work in the labs. This helps determine if the evidence was contaminated.

Toxicology Laboratory

Forensic Toxicologists test human fluids and tissues to determine the presence of drugs, and other chemical substances. Normally, the Medical Examiner draws about 2 mL of Vitreous Humor, 30 mL of blood, and 30 mL of urine from each body and sends it to Toxicology for analysis. Vitreous Humor is the clear fluid inside the eye that gives the eye its shape. Toxicologists sometimes analyze it to confirm results from the blood or urine. Blood transports oxygen, nutrients and other chemicals throughout a person’s body. Most chemicals ingested into the body will quickly appear in a person’s blood stream. Urine is one of the main ways toxins and other chemicals are removed from the body. Sometimes toxicologists analyze stomach contents or maggots found in a decomposing body. Maggots in a decomposing body ingest any chemicals that are present in the body. Testing maggots can be very useful if a body is too decomposed to collect the standard toxicology samples. The stomach contents contain any undigested food or liquids a person ate before they died. Analyzing these contents helps determine what, when, and sometimes where a person last ate. Analyzing stomach contents also tells us how a chemical got into the body (was it a powder, a pill...) If a chemical is found in the blood but not in the stomach, it may have been injected. Almost any fluid in the body can provide evidence of what a person has injected. Looking at multiple fluids helps prevent error and contamination. If a drug is present in one part of the body, it should be present in others. To analyze an evidence, first, we screen the samples for certain types of drugs. We screen for alcohol using Headspace Gas Chromatography. Any alcohol in the sample will evaporate into the headspace, where we can analyze it. Then, an Elisa Test can tell us if certain types of drugs (for example amphetamines, barbiturates, opiates) are present in the sample. However it can’t identify specific individual chemicals. During an Elisa test, the samples change color when a drug is detected. Scientists use positive controls (samples that purposely contain a certain drug) and negative controls (samples that purposely do not have the drug) to ensure it is working correctly. All the samples and controls are also replicated twice to help make sure no mistakes are made. Screening tests like Elisa can only identify classes of drugs. To find out the exact drug, we need a different test. We can use the Gas Chromatograph/Mass Spectrometer (GC/MS) to confirm the specific drugs that were in the victim’s system. The GC/MS separates the chemicals in a specimen and then identifies each one. A graph of the data, called a mass spectrum, is generated for each chemical found in the specimen. Each chemical has its own specific mass spectrum, it is unique. Now we identify the mass spectra from the blood.

Firearms and Toolmarks

A Semiautomatic handgun fires a single cartridge, ejects the spent cartridge case, and reloads itself each time the trigger is pulled. A separate

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