In forensic hair examination, mitochondrial DNA analysis is preferred over nuclear DNA for telogen phase hair shafts. The microscopic feature that BEST distinguishes human hair from dog hair is:
- A Medullary index > 0.5 in dog hair versus < 0.3 in human hair
- B Dog hair shows a continuous ladder-like medulla pattern; human hair medulla is discontinuous, fragmented, or absent with medullary index < 0.33 ✓
- C Presence of a continuous medulla in human hair versus amorphous or absent medulla in dog hair
- D Human hair cuticle scales are imbricate (overlapping forward), while dog hair cuticle scales are coronal
Explanation
Human hairs typically have a medullary index (medulla diameter / shaft diameter) of < 0.33 and the medulla is absent, fragmented, or discontinuous. Domestic animals including dogs have a medullary index > 0.5, with a continuous ladder-like or multiserial medulla. The cuticle scale pattern (coronal vs. imbricate vs. spinous) is another differentiating feature. Coronal scales are found in fine body hair of some animals. Human hair cuticle scales are flat imbricate but this alone does not distinguish dog from human; the medulla pattern is the primary distinguishing feature.
Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.
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Written and medically reviewed by the StethoPrep medical team.