Link to our lab as a pdf - College of Science - Marshall University

Forensic DNA Technology
are the common ones. Those rare alleles in the
population are collectively known as ‘off ladder’ alleles
and are not included. A compilation of these
STR comparisons from as may as 16 different, independent
STR loci make up an individual’s genetic
profile.
Genetic profiles are created for both unknown
samples from a crime scene and those that are obtained
directly from a person who may be a suspect.
Those taken from people, whether they are a suspect,
victim, or any other individual, are referred
to as “knowns.” They are used to compare known
profiles against evidence profiles. An individual is
excluded as a suspect when their profile does not
exactly match the questioned sample’s profile; they
are included only when the fragment sizes are identical
at every STR locus in the DNA.
illustrated a step forward in this rapidly evolving
discipline. As technology and laboratory technique
grow together, further innovations in the science of
determining unique identity are assured.
Additional Reading
Butler, J.M. (2005) Forensic DNA Typing: Biology,
Technology, and Genetics of STR Markers (2nd
Ed). Elsevier Academic Press, New York.
National Research Council (1996) Evaluation of Forensic
DNA Evidence. National Academies Press,
Washington D.C.
STR DNA typing is an examination of the length of
certain repetitions in a genome. In order to weigh
the importance of each match, the final step in DNA
typing is a statistical analysis. By sampling a large
number of people in a particular population, researchers
have determined allelic frequencies for
the STR loci used in forensic DNA typing. By multiplying
the population frequencies of the alleles
present in a genotype, the probability of another
person in a population having the same alleles at
each loci can be determined. As the number of loci
in the analysis increases, the probability of a random
sample matching decreases geometrically.
Thus, the probability is the result of both the rareness
of the individual alleles, the distinctiveness of
their combination, and the number of different STR
loci compared.
Siblings, however, will not share the same statistically
random chance of receiving their alleles, since
they can only receive the alleles their parents possess.
Therefore, it may require testing of many additional
STR loci to separate siblings using DNA typing.
Further, identical twins share identical DNA
and cannot be separated.
DNA analysis has revolutionized forensic identification.
Each of the technologies outlined here have
The Mystery of Lyle and Louise 17