130 Forensic dentistrysolution. Separation of the DNA from the cellular debris and sol-
vents is achieved by alcohol precipitation, filtration, or use of silica
or paramagnetic beads.
Gene: Any segment of DNA that is transcribed into ribonucleic acid and
eventually into a functional or structural protein is called a gene.
Most segments of DNA targeted during forensic analysis are believed
to have little or no structural or functional role.
Genome: The full genetic makeup of an organism is called its genome.
The human genome is composed of 3 billion base pairs and 20,000
to 25,000 genes.
Genotype versus phenotype: The sum of genetic information in an organ-
ism’s genome is its genotype. The physical manifestation of that
genetic information is called the organism’s phenotype.
Locus: The location of a particular gene or segment of DNA is called the
locus (plural: loci). A locus can be described by using the chromo-
some number, designating the short or long arm of the chromosome,
and the band or subband on that arm.
Mitochondrial DNA: Mitochondria are organelles that exist outside the cell
nucleus in the cytoplasm. Mitochondria possess their own genome
that is separate and distinct from the twenty-three pairs of chromo-
somes inside the cell nucleus. The human mitochondrial genome is
16,569 base pairs in length, carries 13 coding regions, and is inherited
along maternal lines. It contains known regions of diversity that help
forensic analysts to distinguish individuals of different maternal
lineages from one another.
Mutation: An alteration in DNA coding sequence that is usually errone-
ous and occurs during DNA replication. It may be caused by an
environmental influence, viruses, or simply a copying error during
cell division.
Nuclease: Enzymes that digest nucleic acids and nucleotides are called
nucleases. These proteins occur naturally in many microbial con-
taminants, and although human-specific primers will not recognize
and amplify the bacterial genome, the nucleases within the bacteria
can degrade the human DNA sample.
Nucleic acid: A long chain of five-sided sugar rings, nitrogenous bases, and
phosphate connectors is a nucleic acid. The structural unit of the
molecule is called a nucleotide. Without the phosphate group, the
molecule is called a nucleoside.
PCR: The polymerase chain reaction is a laboratory technique that targets
a specific segment of original DNA template placed in the appro-
priate chemical environment along with primers, polymerase, and
nucleotides. During a series of carefully orchestrated temperature
changes, the template undergoes denaturization, annealing, and