Service | Function | Method |
---|---|---|
Crime scene investigation | Evidence recognition, documentation, collection, and preservation. | Crime scene responses and related endeavors are diverse and vary with case and type of evidence. |
Latent print examination | Analysis of friction ridge detail in fingerprints. \n Activities include visualization, recording, comparison, storage, and recovery of latent prints, | Alternate light sources, and physical (powder) and chemical enhancements. Direct lifts, photography, and digital imaging. \n Use of an Automated Fingerprint Identification System (AFIS) database. |
Forensic biology | Identification of biological fluids (blood, semen, and saliva).DNA profiling for individualization. | Serological and biochemical methods. \n Polymerase chain reaction (PCR)-based methods. Automated electrophoresis platforms. Use of Combined DNA Index System (CODIS). |
Controlled substance analysis | Identification and quantification of drugs present in submitted evidence. | Microscopic, chemical, chromatographic, and spectroscopic methodologies. Gas chromatography–mass spectrometry or infrared spectrophotometry. |
Postmortem toxicology | Determination of concentrations of substances and their metabolites in biological fluids or tissues. | Immunoassays and chemical methods. Confirmatory techniques such as gas and liquid chromatography–mass spectrometry. |
Questioned document examination | Investigation of forgeries, tracings, disguised handwritings, computer manipulation of images, and recovery of altered documents. \n Analysis of papers, inks, toners, word processors, typewriters, copiers, and printers. | Macroscopic and microscopic comparisons. Chromatographic and spectroscopic methods. |
Firearm and toolmark examination | Identification of firearms, tools, and other implements (expertise achieved predominantly through experience). | Microscopic comparisons of questioned and authenticated impressions. Comparison of striae on recovered bullets.Use of the National Integrated Ballistics Information Network (NIBIN). |
Explosive and fire debris examination | Identification, recovery, and detection of bulk explosives, residues, debris, and accelerants. | Microscopic, spectroscopic, and chromatographic methods. Gas chromatography–mass spectrometry may be needed to adequately characterize the sample. |
Trace evidence examination | Analysis of transferred evidence such as hairs, fibers, soil, paints, and glass. | Microscopic analysis of evidence with gas chromatograph-mass spectrometers, FTIR microscopes, scanning electron microscopes, basic and advanced microscopy, and capillary electrophoresis. |
The human genome contains all the necessary biological information for cellular and organ structure and function.
The human nuclear genome, a set of 23 chromosomes, contains approximately 3 billion base pairs.
The Human Genome Project was initiated in 1990 to sequence the entire human nuclear genome.
The genome contains genes and intergenic noncoding sequences.
\
Approximately 20,000–25,000 genes have been identified in the human genome, which encode the information for the synthesis of proteins.
The coding regions of genes are called exons and are separated by introns.
During gene expression, the precursor messenger RNA transcript, consisting of both the exons and introns, is produced.
Through the process of splicing, the introns are removed and the exons are joined, producing the spliced mRNA form, which can be used for protein synthesis via the translation process.
Other gene-related sequences include those responsible for gene transcription such as promoter sequences; those responsible for gene regulation such as cis-regulatory sequences and untranslated sequences, which are transcribed but do not encode proteins.
\
Tandem Repeats: Repeat units placed next to each other in an array.
\
Interspersed Repeats: Randomly located throughout the human genome.
Transposition: The mobile elements change their locations.
During transposition, DNA transposons are excised from one site and inserted at a new site in the genome.
Retrotransposons duplicate themselves during transposition and propagate throughout the genome, which is a copy-and-paste mechanism: a copy of the original retrotransposons is generated at the new site and the original copy is retained.
Retrotransposition: The transposition of retrotransposons which requires an RNA intermediate.
Long Term Repeat Retroposons
Non-LTR Retroposons
\
\
DNA polymorphisms: The differences between individual genomes that occur at the DNA level.
Sequence Polymorphisms: A DNA polymorphism with alternative forms of a chromosomal locus that differ in nucleotide sequence.
Lengthy Polymorphisms: A DNA polymorphism that differs in the numbers of tandem repeat units.
Many DNA polymorphisms are useful for genetic mapping studies and hence are called DNA markers.
Alleles: Alternative forms of DNA polymorphisms.
Homozygous: The same allele is present in both homologous chromosomes.
Heterozygous: Two different alleles present in homologous chromosomes.
Genotype: A combination of alleles at a given locus.
DNA Profile: The genotype for a panel of analyzed loci.
\
In 1984, Sir Alec Jeffreys developed a DNA profiling technique using a VNTR technique involving multi-locus profiling and later followed by single-locus profiling.
The case was the first to apply DNA evidence to a criminal investigation. During the investigation, DNA profiling not only identified the true perpetrator but it also excluded an innocent suspect.
The most important ability of the technique is to reveal far greater individual variability in DNA than can be revealed by antigen and protein polymorphic markers.
In the mid-1980s, Kary Mullis and his coworkers developed the polymerase chain reaction (PCR) technique, which amplifies a small quantity of DNA.
The application of PCR-based assays makes forensic DNA analysis possible when only minute quantities of DNA can be recovered from a crime scene, for example, from hairs and cigarette butts.
In 1995, the United Kingdom established the first national DNA database for criminal investigations.
By the end of 1998, several other countries, including the United States, had created their own national DNA databases.
mtDNA: It is maternally inherited genetic material and is therefore particularly useful for human identification.
Y-chromosomal markers: These are paternally inherited so they can be used for paternity testing.
\n