History and Development of Forensic Biology

Karl Landsteiner’s work on ABO blood groups around the start of the twentieth century helped explain why blood from different people was not interchangeable. In forensic testing, a readable group could exclude a proposed donor with an incompatible type. Agreement meant that the person belonged to a group shared with other people; it did not identify the individual.

ABO antigens are carbohydrate structures carried on red-cell surface molecules. Secretor status affects whether ABH substances can be detected in certain body fluids. Later serological work also used other inherited markers, including enzyme variants. Combining informative results could narrow the possible donor pool, subject to the marker frequencies, inheritance and sample condition.

No single worldwide percentage describes the frequency of group O or A: frequencies depend on the population. Nor is there a universal match probability for a collection of historical markers. A report needs the actual results, appropriate reference data and justified assumptions.

Body-fluid screening and donor typing are different tasks. A reaction suggesting blood or semen addresses the possible nature of a stain; an inherited marker comparison addresses possible donors. Modern DNA testing did not eliminate the need to investigate which material was sampled or how it was deposited.

Alec Jeffreys and colleagues at the University of Leicester developed DNA fingerprinting in 1984 and published foundational work in 1985. The early approach examined highly variable minisatellite regions. Restriction digestion cut DNA, electrophoresis separated fragments, Southern blotting transferred them to a membrane, and labelled probes revealed variable band patterns.

This combination is often described as RFLP-based DNA profiling. The result depended on the material, enzymes, probes and detection system; it was not the same data format as a modern capillary-electrophoresis STR profile. Large fragments required sufficiently intact DNA, making heavily fragmented material difficult to analyse.

A 1985 immigration dispute was an early practical application to biological relationships. In the Leicestershire murder investigation that followed, DNA comparisons excluded an initial suspect who had confessed and supported the investigation that identified Colin Pitchfork. His conviction followed in 1988. The case illustrates the value of excluding an incompatible suspect as well as investigating a compatible result.

There is no reliable universal rule that a stain must be larger than a particular coin for RFLP to work. Quantity, molecular integrity, extraction yield and the assay all matter. Historical statements about sample requirements should describe these constraints rather than promise a fixed minimum stain size.

PCR, developed in the 1980s, copies selected target sequences through repeated denaturation, primer annealing and extension. It does not recreate a target that has been lost or repair every damaged molecule. Its forensic value includes analysis of shorter surviving regions from material unsuitable for earlier large-fragment methods.

Early PCR typing included HLA DQA1. STR multiplexes subsequently allowed several repeat regions to be amplified together. Capillary electrophoresis estimates product sizes; allele calls describe the observed variants under the validated system. Low-template samples remain vulnerable to allele dropout, imbalance and contamination.

The FBI distinguishes CODIS, the database software/programme, from NDIS, its US national index. NDIS became operational in 1998. The original 13 core STR loci expanded to 20 from January 2017. This is a US database specification, not a fixed worldwide number of loci or a guarantee that every submitted profile contains all of them.

The UK National DNA Database began in 1995. Database systems can connect an eligible questioned profile to a reference or another case, but a candidate association requires the prescribed confirmation and case assessment. Database eligibility, retention and deletion are governed by the applicable system and law.

An improved method is useful only if relevant material remains and its history can be assessed. Blood, semen, saliva, contact traces, hair, bone and teeth offer different targets and different preservation problems. Human nuclear DNA in blood comes mainly from white cells, not mature red cells. Contact DNA need not consist only of intact skin cells.

Rootless hair can contain fragmented nuclear DNA. Conventional STR testing may be uninformative even when other nuclear or mitochondrial methods can recover useful data. Mitochondrial testing has long been important for hair, but the choice should reflect the specimen and validated capability rather than an absolute rule that a rootless shaft has no nuclear DNA.

Keep contamination prevention, packaging and storage separate from expectations about test sensitivity. Dry stained items generally need appropriate drying and breathable packaging; liquid specimens and wet items require their own leakproof, temperature-controlled procedures. Avoid a blanket instruction to freeze all liquid blood or put all biological material into paper.

An old evidence store should be assessed for seals, identifiers, packaging, temperature history, prior sampling and remaining quantity. There is no universal survival deadline such as a fixed number of hours outdoors. An apparent negative result may reflect degradation, inhibition, low quantity or the limits of the method, rather than absence of relevant material.

A typical diploid human nucleated cell has 46 chromosomes arranged in 23 pairs. One haploid chromosome set contains roughly three billion base pairs; a typical diploid nucleus contains about twice that amount before replication. Mature red cells, gametes, dividing cells and abnormal chromosome complements require more specific descriptions.

STRs vary in repeat number. A comparison uses the actual observed alleles and an appropriate statistical model. Non-coding does not mean that every such region has no biological function or is free from all selective effects. The reason to select a forensic marker includes its variation, assay behaviour and suitability for the intended comparison.

Mitochondrial DNA has a different copy number and inheritance pattern from autosomal DNA. Higher starting copy number can help recovery from some compromised specimens; it does not make mitochondrial molecules immune to degradation. Maternal relatives may share a sequence, while heteroplasmy and mutation complicate an absolute claim that all such relatives must be identical.

Y-chromosome markers follow paternal inheritance in the usual case and often cannot distinguish close paternal-line relatives. Autosomal, mitochondrial and Y results answer different comparison questions. A lineage association must not be reported with the discrimination expected from a suitable full autosomal profile.

Massively parallel sequencing can examine STR sequence variation, SNPs or mitochondrial targets, depending on the assay. Sequence information may distinguish alleles of the same length. It does not make every mixture easy to resolve, guarantee success with degraded evidence or produce a universal best identification method.

Forensic genetic genealogy usually requires SNP information suitable for the relevant database. Investigators combine permitted database comparisons with documentary family research to develop leads. An STR allele list cannot simply be converted into thousands of previously unmeasured SNP genotypes. New testing of retained extract or material may be necessary, and it may fail.

The US Department of Justice published an interim forensic genetic genealogy policy in 2019 for work within its scope. It is not a worldwide permission to search consumer databases, nor a complete statement of every US state’s rules. In the UK, the separate legal systems and relevant database rules matter. In India, the DNA Technology Regulation Bill, 2019 was withdrawn in July 2023; it must not be described as an enacted DNA Act.

Scientific review also examines how results are communicated. A donor comparison, a proposed transfer mechanism and a conclusion about an offence require different reasoning. Admissibility rules vary by jurisdiction. A new instrument or a database lead does not remove the need for validation, quality controls, uncertainty and a justified report.