ETC Biological & DNA Evidence Flashcards
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Read the first 6 ETC Biological & DNA Evidence flashcards as text
What is Locard's principle as it specifically applies to biological transfer evidence?
Answer: When two individuals have contact, biological material such as hair, skin cells, and blood is exchanged between them
Locard's Exchange Principle in biological evidence means that physical contact results in transfer of biological material like DNA, hair, and skin cells between persons and objects.
When collecting hair evidence, what is the minimum number of hairs typically required for comparison purposes?
Answer: At least 15–25 representative hairs from multiple areas of the scalp for reference samples
Reference hair samples require 15–25 representative hairs from multiple scalp regions to capture the natural variation in hair characteristics for comparison.
What does a positive result from a phenolphthalein (Kastle-Meyer) test indicate?
Answer: Presumptive presence of blood (hemoglobin catalyzes the reaction to produce pink color)
The Kastle-Meyer test uses phenolphthalein; hemoglobin acts as a catalyst causing the reagent to turn pink, indicating a presumptive positive for blood.
Which condition is most likely to degrade DNA quality in biological evidence collected from an outdoor crime scene?
Answer: Prolonged exposure to UV light, heat, and humidity
UV radiation, heat, and humidity are the primary environmental factors that cause DNA fragmentation and degradation in outdoor biological evidence.
What is the difference between nuclear DNA and mitochondrial DNA in forensic evidence applications?
Answer: Nuclear DNA provides individual identification; mitochondrial DNA provides maternal lineage but is not individually unique
Nuclear DNA contains unique individual genetic information, while mitochondrial DNA is inherited maternally and shared among maternal relatives, providing lineage but not individual identification.
When collecting swabs from multiple locations at a crime scene for biological evidence, why must a new swab be used for each location?
Answer: To prevent cross-contamination between locations, which could produce mixed DNA profiles and confuse the investigation
Using a separate swab for each location prevents cross-contamination, which could create mixed DNA profiles that make it impossible to determine which DNA came from which location.