128 Forensic dentistryAmplicon: The amplified segment of DNA that is the product of PCR is
called the amplicon. The two boundaries of this target DNA are
usual marked by forward and reverse primers before the PCR pro-
cess begins.
Amplification: The process of increasing the quantity of original DNA
template by using the polymerase chain reaction (PCR) is referred
to as DNA amplification.
Analysis: The third step in laboratory processing is called analysis. Once
a DNA sample has undergone extraction and amplification and is
loaded into a genetic analyzer, data are generated that represent
either a genetic profile based on the size of the alleles at each locus
tested (autoDNA, yDNA) or the actual sequence of the targeted DNA
(mtDNA). The raw data are then reviewed by the analyst, who uses his
education, training, and experience to confirm the result and, when
appropriate, compare sets of data, draw conclusions, and calculate
statistical values. Some laboratories call the instrumentation portion
of this process detection and reserve the word analysis for the final
data review step by the analyst only.
Bases: DNA is composed of nucleotides strung together in a twisted double
strand. Nucleotides are ring-shaped molecules with various combi-
nations of carbon, oxygen, hydrogen, and nitrogen with a phosphate
group attached. The nitrogen-containing portion of the nucleotide is
called a base. Differences in base design result in four variations of
bases in DNA: adenine (A), guanine (G), thymine (T), and cytosine
(C). The distinctive sequence in which these four bases occur within
specific locations along the DNA strand provides the genetic code for
protein production, as well as the power of individualization used by
the forensic scientist.
CODIS and NDIS: The Combined DNA Index System (CODIS) is a soft-
ware application that was developed and distributed by the Federal
Bureau of Investigation. The software allows the storage and search-
ing of large amounts of DNA data. Crime laboratories that qualify for
CODIS access at the local, state, and national levels can search their
own profiles and, more significantly, also search the DNA profiles
posted by other laboratories through the shared data in the National
DNA Index System (NDIS).
Complementary: In its natural configuration, DNA is double stranded. In
the successful pairing of two single strands, the opposing sequences
must be complementary. This means that adenine will only align
opposite thymine, and guanine will align exclusively with cytosine.
If the sequences within the opposing segments of DNA do not
meet these exacting requirements, regardless of their length, the
single strands are not complementary and will not pair together.