Semen, Saliva and Other Body Fluids as Evidence

Semen combines sperm, where present, with secretions from accessory glands and other cellular or extracellular material. The seminal vesicles and prostate make major contributions. PSA, also called p30, and semenogelins are useful associated protein targets; acid phosphatase activity supports screening under appropriate procedures.

A spermatozoon has a head with a haploid nucleus, an acrosomal region, a midpiece containing mitochondria and a flagellar tail. A mass of sperm from one donor can provide both of that donor’s inherited alleles across the population of cells, even though each sperm is haploid. A stain’s measured profile is not necessarily the profile of one sperm.

Microscopy can identify sperm morphology with suitable staining. Christmas tree staining uses nuclear fast red and picroindigocarmine, not a haematoxylin-based formulation. Nuclear regions appear red and tails or other cellular components may appear green under the relevant method. Damaged or isolated heads need competent assessment.

Azoospermia means absence of sperm in the ejaculate. Vasectomy does not immediately or invariably produce a sperm-free specimen; residual sperm, failure or recanalisation can matter. Conversely, an unsuccessful sperm search can reflect sampling, degradation, washing or low abundance, rather than a known donor condition.

PSA detection can remain informative without observed sperm, but low-level PSA can occur outside semen and assay behaviour matters. Fluorescence is a search aid, not semen identification. No single negative test reliably excludes every possible semen-containing specimen, and a positive marker does not establish a particular sexual activity.

Saliva contains glandular secretions and material from the mouth, including epithelial cells, leukocytes, microbes and extracellular molecules. Cellular content varies substantially; no single fixed cell count per millilitre predicts the DNA yield of a cigarette end or glass rim.

Salivary alpha-amylase hydrolyses starch. Activity tests can locate areas consistent with saliva, but amylase also occurs elsewhere and the reaction is not human-specific. Phadebas releases blue dye when dye-linked starch is digested. An immunological test may target human salivary amylase, with specificity and cross-reactions assessed for that assay.

Drinking vessels, smoked items, masks, adhesive surfaces and suspected saliva on skin are possible collection targets. An object may also carry handling DNA or material from more than one user. A DNA profile on a glass does not independently prove that its donor drank from it.

A validated wet-then-dry swab method can be useful on suitable surfaces; it is not guaranteed to maximise recovery in every case. Photograph relevant marks before sampling and coordinate other examinations. The presence of a suspected bite mark does not make morphological identification of a biter scientifically reliable.

Vaginal material can contain epithelial cells, mucus, transudate, microbes and secretions from connected or nearby structures. Cell appearance and collection location can inform context but do not uniquely establish the fluid on an unrelated object. RNA, methylation and microbial approaches have different levels of validation and use; there is no universal single-marker solution.

Sweat is produced by eccrine and apocrine glands and can accompany DNA-bearing material on skin or clothing. Surface corneocytes are often anucleate, but contact deposits may contain cell-free DNA and other cellular material. It is too absolute to say that anucleate material can contribute no recoverable DNA.

Urine is formed through filtration, reabsorption and secretion, rather than simply being unchanged filtered plasma. Its potential DNA yield depends on cells, cell-free material and specimen condition. Creatinine or other chemical markers are not perfectly specific fluid identifiers. A urine-associated genetic result still requires a qualified donor comparison.

Scene collection begins with documentation and a sampling plan. Photograph locations before disturbance, use appropriate protective measures and DNA-controlled tools, and separate items. Consider whether recovering the whole item will preserve context and permit better laboratory sampling than cutting a fixed-size swatch at the scene.

Dry stained items generally need separate, suitable breathable packaging and protection from moisture. Wet items require controlled drying where appropriate or a receiving-laboratory plan for prompt cold transport and storage. Liquid specimens need leakproof containment. Neither “all wet swabs go into transport medium” nor “all samples must be frozen after drying” is a universal rule.

A substrate comparison can help assess background from a surface, but is not obligatory in an identical form for every specimen. It cannot identify every source in a mixture or be subtracted automatically. Collection blanks, reagent blanks and known references answer other questions and are not interchangeable controls.

Intimate examination and clinical specimen collection require trained practitioners, appropriate consent or other applicable authority and patient-centred procedures. Medical care must not be treated as secondary to evidence gathering. Follow the applicable clinical protocol rather than imposing a universal swab order or collection deadline.

Record identifiers, locations, seals, handlers, timing, storage and relevant departures. Reference samples require a justified purpose and lawful collection. Requirements vary by jurisdiction and case; a generic statement about one evidence Act is not a substitute for the applicable procedure.

Temperature, moisture, light, microbes, substrate and protection influence recovery. Biological molecules can remain detectable for long periods in some dry stains, while other specimens change rapidly. There is no universal 72-hour survival limit or fixed percentage of sperm lost in a machine wash.

Washing can remove, dilute, redistribute or alter biological material. Some targets can remain detectable, and DNA transfer between items can occur during laundering. Findings on a washed garment need assessment of that history rather than an assumption that washing either removes everything or proves recent deposition.

Ultraviolet damage can create photoproducts between adjacent bases on the same DNA strand. It should not be described simply as crosslinking the two strands. Physical removal, backbone fragmentation and chemical base damage are different processes, although more than one can affect a sample.

DNA and fluid markers do not necessarily persist together. A partial profile or negative marker result needs assessment of quantity, inhibition, degradation and method sensitivity. Neither a positive marker’s intensity nor a degradation index provides a validated exact date of contact.

Differential extraction uses differences in cell lysis to enrich sperm and non-sperm DNA fractions. Conventional methods first release much non-sperm material, then treat the retained material under conditions that lyse resistant sperm heads. Performance depends on the specimen, degradation and procedure.

The fractions are enrichment products, not automatically a complainant profile and an offender profile. Carryover, non-sperm DNA from a semen donor, multiple sperm contributors and preferential recovery can all matter. A fraction label does not establish the contributor’s role or fluid source.

Interpret each profile with its controls, quality, mixture assessment and relevant propositions. A sperm-associated genetic comparison can inform a donor question without establishing penetration, timing or consent. If the disputed issue is activity rather than donor identity, transfer, persistence, background and competing explanations may require a separate supported assessment.

US national medical-forensic guidance and England-and-Wales forensic medical guidance provide examples of jurisdiction-specific procedures. India, Canada, Australia and other jurisdictions have their own applicable requirements. Teach the shared scientific distinctions first, then use the procedure governing the case rather than assuming one country’s rules apply worldwide.