Determination of Species of Origin from Blood and Body Fluids

Species of origin sits between the confirmatory test for blood (Takayama, Teichmann) and the individualising DNA profile. Until the analyst can certify that a stain is human, no downstream DNA work proceeds and the chain of evidence breaks at the trial stage. In a homicide case the question is binary: human or not. In a wildlife case the question expands to which protected species, which decides the schedule under the Wild Life (Protection) Act 1972 and the punishment under Section 51.

Three casework streams demand species ID. First, criminal investigations where a suspect claims that blood on his clothing came from a chicken or goat slaughtered at home. Second, poaching cases where seized meat, hide, horn or claw must be tied to a Schedule I species (tiger, leopard, pangolin, gharial). Third, food adulteration cases under FSSAI where mutton or beef is mislabelled. The same toolkit serves all three.

The original Uhlenhuth precipitin test is a layered tube reaction. The analyst extracts the bloodstain in saline, clarifies the extract, and gently layers it over anti-human serum in a capillary tube. A white precipitin ring at the liquid interface within five to thirty minutes is a positive result. Paul Uhlenhuth introduced this in 1901 and it was used in the same year to convict Ludwig Tessnow in Germany, the first criminal conviction based on the precipitin reaction. The test detects as little as a microgram of species-specific serum protein and works on stains decades old.

Ouchterlony double diffusion (1948) moved the same reaction into agar. Wells are punched in an agar plate; the unknown blood extract goes in the centre well, and anti-human, anti-bovine, anti-canine and anti-caprine sera go in surrounding wells. Antigen and antibody diffuse outward; a sharp precipitin line forms only between the centre well and the matching antiserum well. The advantage is that several species can be screened in one plate, and the geometry of the precipitin lines (identity, partial identity, non-identity) confirms cross-reactivity.

A reasonable companion read is the antigen-antibody principle covered earlier in Unit II, since every species-of-origin reaction rests on the same chemistry. The species-specific antiserum is the reagent that turns a general immunology technique into a forensic identification tool.

Crossover-electrophoresis (also called counter-immunoelectrophoresis, CIEP) puts antigen and antibody in adjacent wells of an agar gel and applies a current at a pH where the antigen migrates anodally and the antibody migrates cathodally. The two reagents meet in the middle within twenty to forty minutes and form a precipitin line at the zone of equivalence. CIEP is roughly ten times faster than passive Ouchterlony diffusion and an order of magnitude more sensitive.

Immunoelectrophoresis (Grabar and Williams, 1953) is a two-step technique. Antigens in the unknown extract are first separated by electrophoresis according to charge. A trough cut parallel to the migration lane is then filled with antiserum, and the antibodies diffuse laterally into the gel. A series of precipitin arcs form, each arc identifying one species-specific antigen. The pattern of arcs gives more discriminating information than a single Ouchterlony line, and is especially useful when a sample is suspected to contain blood from two species.

For the underlying gel and voltage chemistry, cross-reference the electrophoresis and immunoelectrophoresis topic in Unit II. NTA likes to test the bridge between Unit II technique and Unit III application, so the same MCQ may appear under either bullet.

Classical precipitin tests assume the species-specific protein has survived intact. Heated, buried, putrefied or chemically treated samples may have no usable protein left. Mitochondrial DNA is more robust because each cell carries hundreds to thousands of mitochondrial copies, and the mitochondrial cyt-b gene is conserved enough at the primer sites to amplify across mammals while variable enough in the middle to discriminate species.

Cytochrome-b (cyt-b) PCR is the standard workflow. Universal mammalian primers amplify a 350 to 400 base-pair fragment of the cyt-b gene. The amplicon is sequenced by Sanger or by next-generation sequencing, and the sequence is compared against GenBank using BLAST. A match of 98 percent identity or higher with a single reference species is reported as a positive identification. Cyt-b works on bloodstains, hair shafts, hide fragments, cooked meat and even tannery-processed leather.

Cytochrome c oxidase subunit I (COI, sometimes COX1) is the formal DNA barcode for animals under the BOLD (Barcode of Life Database) initiative. COI is preferred for wildlife casework because the BOLD reference library is curated for taxonomic accuracy, unlike GenBank which accepts submissions without verification. For Indian wildlife species the National Centre for Cell Sciences and the Wildlife Institute of India have built supplementary COI reference panels.

For severely degraded samples a third option, 12S or 16S ribosomal RNA mini-barcoding, amplifies fragments under 150 base pairs. This is the workflow of choice for ivory, rhino horn powder, and traditional medicine seizures where DNA is fragmented to ribbons.

In India the species-of-origin workload is split across three institutional anchors. The CFSL DNA divisions, most prominently at CFSL Hyderabad under DFSS, handle human versus animal questions in criminal cases and run both serological (Ouchterlony, CIEP) and molecular (cyt-b PCR) workflows. State FSLs in Maharashtra, Karnataka and West Bengal also house serology sections that perform routine precipitin tests on case material.

The Wildlife Institute of India (WII) at Dehradun runs the Wildlife Forensic and Conservation Genetics Cell, which is the apex authority for poaching cases. WII issues species-identification certificates that are admissible in trial under the Wild Life (Protection) Act 1972 and maintains India's largest reference DNA collection for Schedule I species.

The Laboratory for the Conservation of Endangered Species (LaCONES) at CCMB Hyderabad, set up in 1998 by the CSIR-Centre for Cellular and Molecular Biology, is the second wildlife genetics centre of national stature. LaCONES specialises in cyt-b and COI sequencing for endangered species, holds frozen-tissue archives, and supports the Ministry of Environment, Forest and Climate Change on cross-border wildlife trafficking. Between WII Dehradun and CCMB LaCONES, the bulk of Indian wildlife species-ID casework finds a home.