Biological and Trace Evidence Flashcards

What forensic technique uses the ratio of stable isotopes in human hair to provide information about a person's geographic origin or diet?

Answer: Inductively coupled plasma mass spectrometry (ICP-MS) for stable isotopes

ICP-MS can measure stable isotope ratios (e.g., strontium, oxygen, carbon) in hair, which reflect diet and geographic origin over time.

Which condition best describes how fingernail clippings from a victim should be packaged to preserve potential DNA and trace evidence?

Answer: Air-dried briefly then placed in a clean paper fold (druggist fold) in an envelope

Fingernail clippings should be air-dried and packaged in a paper fold to prevent moisture buildup that could degrade DNA and obscure trace materials.

When analyzing questioned documents for fiber content, which type of microscopy best reveals the three-dimensional surface structure of a single fiber?

Answer: Scanning electron microscopy (SEM)

SEM generates detailed three-dimensional surface images of fibers, revealing surface features, cross-sections, and damage that other microscopy methods cannot.

A bloodstain analyst observes elongated elliptical stains on a wall with one sharp and one ragged edge. What does the ragged (tail) edge indicate?

Answer: The direction of travel of the blood droplet

The tail (ragged edge) of an elliptical bloodstain points in the direction the droplet was traveling when it struck the surface.

Which biological sample collected at a sexual assault scene provides the most direct confirmatory evidence of male DNA contribution?

Answer: Y-STR profile from a sperm fraction of a vaginal swab

Y-STR profiling of the sperm fraction from a vaginal swab provides male-specific DNA directly associated with the assault.

In forensic botany, diatoms recovered from a drowning victim's bone marrow are significant because they indicate what?

Answer: The victim was alive and breathing when submerged, allowing diatoms to enter the bloodstream

Diatoms can only reach bone marrow via circulation, so their presence indicates the victim was alive and inhaling water at the time of submersion.

What is the primary advantage of using mitochondrial DNA (mtDNA) analysis over nuclear STR analysis for hair shaft evidence?

Answer: mtDNA is present in thousands of copies per cell, making it recoverable from degraded or rootless hairs

mtDNA's high copy number per cell makes it recoverable from degraded or telogen (rootless) hairs where nuclear DNA is insufficient or absent.