Spermatozoon (Pl. Spermatozoa)
Definition
The mature male gamete: an oval head (4-5 microns) containing condensed nuclear DNA and an acrosomal cap, a short midpiece containing mitochondria for motility, and a long flagellar tail (about 45-50 microns). Its presence in a stain is definitive evidence of semen.
- Field
- Forensic serology, microscopy
- Head size
- About 4 to 5 microns
- Tail length
- About 45 to 50 microns
- Head contains
- Condensed nuclear DNA, acrosomal cap
- Midpiece function
- Houses mitochondria for motility
Common questions
Why is the intact spermatozoon considered definitive rather than probable evidence of semen?+
Its distinctive three-part morphology, head, midpiece, and tail, is not produced by any other cell type found in casework samples, so a positive microscopic identification is treated as conclusive rather than merely supportive.
Does the nuclear DNA in the head differ from what other cells in a mixed stain contribute?+
The condensed, protamine-packed DNA in the sperm head requires a different extraction chemistry than epithelial cell DNA, which is the basis for differential extraction separating a sperm fraction from a female epithelial fraction in a mixed stain.
Related terms
- Acrosome
- A cap-like organelle covering the anterior half of the sperm head. It contains hydrolytic enzymes used in oocyte penetration. Forensically it appears...
- Azoospermia
- The absence of spermatozoa from ejaculated semen, resulting from obstructive causes (vasectomy, ductal blockage) or non-obstructive causes (testicular failure). Azoospermic semen contains...
- Christmas Tree Staining
- A two-step differential stain using Nuclear Fast Red (Kernechtrot) to stain the sperm head red/pink and Picroindigocarmine to stain the midpiece and...
- Ghost Head (Decapitated Spermatozoon)
- An isolated sperm head separated from its tail, commonly found in aged or dried stains. The head retains its oval morphology and...
- Sperm Reporting Conventions
- Standardised ways to record microscopy results: some labs report a count per high-power field (HPF), others report as present/absent, and some use...