Epithelial Cell Fraction
Definition
The non-sperm cellular material in a sexual assault sample. Contains skin and mucosal cells from both victim and any perpetrator who made contact. The target for profiling when spermatozoa are absent.
- Contains
- Skin and mucosal cells, no spermatozoa
- Context
- Sexual assault sample differential extraction
- Sources
- Victim and any contacting perpetrator
Common questions
Why is the epithelial fraction separated from the sperm fraction in the first place?+
Differential extraction lyses sperm cells and epithelial cells at different rates, allowing the two to be separated into distinct fractions so that a mixed male and female profile from intercourse can be resolved into cleaner individual contributor profiles.
When does the epithelial fraction become the primary target rather than a secondary one?+
When no spermatozoa are recovered, such as cases involving a vasectomised or azoospermic assailant, condom use, or non-penetrative contact, the epithelial fraction becomes the main source for any DNA profile of the alleged perpetrator.
Related terms
- Azoospermia
- The absence of spermatozoa from ejaculated semen, resulting from obstructive causes (vasectomy, ductal blockage) or non-obstructive causes (testicular failure). Azoospermic semen contains...
- Differential Extraction
- A two-step DNA extraction procedure used when a stain contains both sperm cells and non-sperm epithelial cells. The first step lyses epithelial...
- Double-Swab Technique
- A collection method for dried biological stains in which a moistened swab rehydrates and lifts the stain from the surface, followed immediately...
- Timing Window
- The period after an assault during which a specific locus is likely to yield viable foreign DNA. Windows vary substantially by locus:...
- Y-STR Analysis
- Short tandem repeat profiling targeting the male-specific Y chromosome. Used when female victim DNA overwhelms the autosomal profile in a mixture, allowing...