Crime Scene Investigator PCR Basics™ Kit

analysis of this one allele, you were able to exclude 7 suspects. However, you still have
6 possible suspects. Were they all present at the scene of the crime? To answer this
question, you also analyze the D3S1358 locus. Here, you find that 7 suspects have the
D3S1358 genotype 16-17, a genotype which is also present at the crime scene. Of those
7 suspects, 4 of them also have a TH01 genotype of 6-3. By combining these two genotypes,
you can exclude 2 more suspects, and increase your power of discrimination. To be able to
tell if all 4 of the remaining suspects were present at the crime scene, you also look at the
FGA locus, and discover that the 21-23 genotype is found at the crime scene. In your pool
of suspects, 7 people have that genotype at that locus. However, when combined with the
results from the TH01 allele and the D3S1358 allele, you find that only one of your
13 suspects has the same genotype as was found at the crime scene. Now, after analyzing
3 different loci, you can exclude all but one of your suspects.
Fig. 5. The Power of Discrimination increases as the number of loci tested increases.
As illustrated in these examples, the power of discrimination changes depending on the
loci and the ethnicity of the samples involved in an investigation. This phenomenon presents
special challenges for any investigation! This topic is addressed in more detail in
Appendices B and C.
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