Biological and Trace Evidence Flashcards

Which presumptive test for blood produces a blue-green color change in the presence of hemoglobin?

Answer: Leuco malachite green test

Leuco malachite green (LMG) produces a blue-green color when it reacts with the peroxidase activity of hemoglobin.

What is the primary reason investigators use an alternate light source (ALS) when searching for biological fluids?

Answer: To cause biological fluids to fluoresce or absorb light differently

ALS causes many biological fluids like semen and saliva to fluoresce, making them visible in low-contrast environments.

A fiber recovered from a victim's clothing is identified as nylon. Which microscopic characteristic best distinguishes nylon from polyester fibers?

Answer: Birefringence pattern under polarized light

Polarized light microscopy reveals distinct birefringence patterns that differ between nylon and polyester, aiding fiber discrimination.

When collecting soil evidence, what is the recommended minimum number of reference samples that should be taken from around a scene?

Answer: At least four perimeter samples plus a control

At least four perimeter reference samples plus a control help establish the natural soil variation around the scene for comparison.

Which enzyme is most commonly targeted in confirmatory tests for amylase to identify saliva?

Answer: Alpha-amylase

Alpha-amylase is produced in high concentrations in saliva and is the enzyme targeted in saliva identification assays.

A hair root pulled out forcefully with an intact follicular tag is most useful for which type of analysis?

Answer: Nuclear DNA analysis

A follicular tag contains nucleated cells, providing nuclear DNA suitable for STR profiling.

What characteristic of glass fractures helps determine the direction from which a force was applied?

Answer: Radial and concentric crack patterns with hackle marks on edges

Radial cracks form first and hackle marks on their edges point back toward the origin, revealing the direction of applied force.