Male Fraction (Sperm Fraction)
Definition
The lysate produced by the second (DTT + proteinase K) lysis step after washing the sperm pellet. Ideally contains predominantly the suspect's sperm-cell nuclear DNA.
- Step produced
- Second lysis (DTT + proteinase K)
- Preceded by
- Sperm pellet washing
- Expected content
- Predominantly sperm-cell nuclear DNA
- Companion fraction
- Female (epithelial) fraction, first lysis
Common questions
Why does the male fraction require a second, separate lysis step?+
Sperm cell membranes are chemically resistant due to disulfide cross-linked proteins, so a reducing agent like DTT is needed to break them open after the more easily lysed epithelial cells were already removed in the first step.
Can the male fraction still contain female DNA?+
Yes. Differential extraction rarely achieves perfect separation, so a male fraction can carry residual female DNA, particularly when sperm counts are low, which analysts account for when interpreting mixed profiles.
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...
- Female Fraction
- The lysate produced by the first (no-DTT) lysis step of differential extraction. Contains DNA from epithelial cells and other non-sperm cellular material...
- 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...
- 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...