Female Fraction
Definition
The lysate produced by the first (no-DTT) lysis step of differential extraction. Contains DNA from epithelial cells and other non-sperm cellular material from the victim.
- Produced by
- First (no-DTT) lysis step
- Contains
- Epithelial and non-sperm cellular DNA
- Context
- Differential extraction, sexual assault casework
Common questions
Why does the female fraction need to be isolated separately rather than just extracting DNA from the whole swab?+
In a sexual assault swab, victim epithelial cells and donor sperm cells are mixed together. Without separation, the resulting DNA profile would be an uninterpretable mixture, so isolating the epithelial-dominant female fraction from the sperm-dominant male fraction lets each be profiled cleanly.
Can the female fraction still contain some male DNA, and does that undermine the method?+
Yes, incomplete cell lysis or sperm cell rupture can leave trace male DNA in the female fraction. This is a recognized limitation of differential extraction, which is why examiners interpret female-fraction profiles as epithelial-dominant rather than assuming complete separation.
Related terms
- 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...
- DTT (Dithiothreitol)
- A reducing agent that cleaves the disulphide bonds in the sperm protamine matrix, allowing proteinase K and SDS to lyse the sperm...
- Erase Sperm Isolation Kit
- An immunomagnetic sperm-cell isolation system using paramagnetic beads coated with antibodies against sperm-specific surface antigens. Achieves greater than 99% sperm recovery with...
- Laser Capture Microdissection (LCM)
- A UV-laser instrument technique for physically isolating individual cells or clusters of cells from a stained slide into a capture tube, without...
- Male Fraction (Sperm Fraction)
- The lysate produced by the second (DTT + proteinase K) lysis step after washing the sperm pellet. Ideally contains predominantly the suspect's...
- Protamine
- Small arginine-rich proteins that replace histones in the nuclei of spermatozoa during spermatogenesis, producing a hyper-compacted chromatin structure approximately six times denser...