Term
| What are class characteristics of a gun barrel? |
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Definition
-Direction of twist
-Number of lands/grooves
-Caliber
-Land width
-Groove width |
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Term
| What are class characteristics and individual characteristics? |
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Definition
Class: measurable features which indicate restricted group sources
Individual characteristics: marks produced by random imperfections or irregularities that are unique to the object |
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Term
| True or false: The best way to determine if tool made a certain mark is to place the tool in the mark and see if it fits |
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Definition
| False. Doing so may make additional marks and contaminate the original evidence |
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Term
| What are the steps involved when collecting a firearm? |
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Definition
| First pick up by knurled or checkered surfaces with gloves and check to see if it's loaded. If so, unload it and account for the ammunition found. Secure the firearm in a box. |
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Term
| What are the two gunshot residue tests and what do the test for? |
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Definition
Greiss: Must be done first due to chemical interference; tests for nitrates (will turn orange)
Sodium Rhodizinate: tests for lead (will turn pink) |
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Term
| What instrument is used to associate firearms to a bullet or casing? |
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Definition
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Term
| True or false: A bullet can be said to come from a specific gun after examining the direction of twist or caliber |
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Definition
| False. A link to a specific gun can only be determined with individual characteristics, not class |
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Term
| What does charred or melted fabric around a bullet hole indicate? |
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Definition
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Term
| What does an firearms examiner use to determine distance from muzzle to target? |
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Definition
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Term
| What is microsil and what is it used for? |
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Definition
| A casting agent that picks up individual characteristics of a tool mark. |
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Term
| What do you use to cast shoe or tire impressions? |
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Definition
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Term
| What part of the gun barrel imparts the most individual characteristics on a bullet? |
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Definition
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Term
| In regards to shotguns, what is a choke? |
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Definition
| Constriction in the barrel to control the spread of shot |
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Term
| How does one determine the caliber of a gun? |
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Definition
| Measure the diameter of the barrel from land to opposite land |
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Term
| What are the sources of impression marks from a firearm? |
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Definition
-Firing pin
-Breachface
-Extractor |
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Term
| What are the sources of stria from a firearm? |
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Definition
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Term
| How long does it take for sperm to start dying off? |
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Definition
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Term
| What is a Woods lamp and what does it do? |
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Definition
| Alternate light source; used to look for semen saliva, vaginal secretions, detergents, and food (which will fluoresce). Preliminary. |
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Term
| Where is the best place to store DNA? |
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Definition
| Freezer, but room temperature storage is fine (and preferable, if there may be fingerprints) |
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Term
| What color is the tube top for collecting blood? |
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Definition
| Purple (yellow MIGHT be ok) |
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Term
| What are some ways to avoid contaminating a scene? |
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Definition
-Wear gloves and change as often as possible
-Wear a mask
-Possibly wear booties
-Don't let anyone in unless necessary
-Use disposable instruments |
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Term
| What are some examples of evidence that can be obtained from a condom? |
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Definition
-Semen
-Sperm
-Vaginal secretions |
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Term
| What is a preliminary test for semen? |
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Definition
| Acid-phosphate (high concentration in semen, low in vaginal secretions) |
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Term
| What test confirms semen even without sperm? |
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Definition
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Term
| What test can find DNA in semen through microscopic examination and is much more stable than Acid-Phosphate or P30 protein? |
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Definition
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Term
| What is the purpose of differential extraction and how is is performed? |
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Definition
| To separate mixed DNA (usually female epithelial cells from sperm cells); epithelial cells are broken open and DNA extracted, while sperm cells are remain intact (DNA can be extracted from head of sperm) |
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Term
| What are the preliminary tests for blood? |
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Definition
-Leucomalachite green
-Hemastix
-Kastle-Meyers
-Luminol |
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Term
| Amylase has very high levels in _______, but can also be found in ________ at much lower levels. |
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Definition
| Saliva; other biological fluids |
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Term
| What are factors that degrade DNA evidence? |
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Definition
-Moisture/humidity
-Ultraviolet light (sunlight)
-Heat
-Dirt, oil, and grease
-Chemicals from cleaning agents, formaldehyde, etc. |
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Term
| How does one collect DNA evidence? |
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Definition
| Either swab the stain (esp. if small), scrape it off (while adhereing to safety precautions), cut out the stained area, or transport the entire item to the lab. Remember to take a control from an unstained area near the stain |
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Term
| How does one preserve DNA evidence? |
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Definition
-Air dry any wet materials
-Package items separately
-Package items in paper bags
-Freeze evidence when possible |
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Term
| How many chromosome pairs do we have? |
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Definition
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Term
| What are the complementary base pairs in DNA? |
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Definition
| Adenine with Thymine and Cytosine with Guanine |
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Term
| Briefly describe how PCR works |
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Definition
| DNA fragment goes through heating cycles and surrounded by primers with complementary DNA fragments so the DNA replicates by many orders of magnitude |
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Term
| What are STRs and how are they used in DNA identification? |
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Definition
| Short tandem repeats (target sequences); After being amplified with PCR, the target STRs are separated and the number of repeats are determined. 16 sites are used for comparison from known and unknown samples. |
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Term
| What are the advantages and disadvantages of Y STRs? |
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Definition
-Useful with very degraded samples with male DNA component
-Useful with multiple male DNA donors
-Useful with mix of female/male DNA
-Useful in "touch" DNA cases with a male component
-Not as good as normal STRs because can be positive for close male relatives |
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Term
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Definition
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Term
|
Definition
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Term
| Mitochondrial DNA can establish _______ connection to unknown sample and can be extracted from a strand of _______ |
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Definition
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Term
| What does CODIS stand for? |
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Definition
| Combined Offender DNA Index System |
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Term
| In what instances are STR profiles uploaded to CODIS? |
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Definition
-Felony offenders
-Solved/unsolved cases (if DNA is known, will be marked with a "z") |
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Term
| What are the circumstances under which a familial search takes place and how often is it successful? What does a familial search involve? |
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Definition
| Needs to be a case where all leads have been exhausted and a DA has to be willing to prosecute; 10% of searches are hits; Y STR DNA profiles |
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