miniPCR bio™ Electrophoresis Forensics Lab. Wrongfully Convicted? Instructor's and Student's Guide
Version: 1.1 - Release February 2022 - © 2022 by miniPCR bio™
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Table 1 shows the allele frequencies for four D7S820 alleles. Scientists have compiled STR profiles
from many individuals selected to represent the entire human population and have used this
information to calculate each allele's frequency. With this information, scientists can calculate the
estimated frequency of every STR genotype.
2. Use the information in Table 1 to calculate genotype frequencies using the formulas above.
Show your work.
A. D7S820 genotype 7, 7
B. D7S820 genotype 7, 9
C. D7S820 genotype 10, 10
D. D7S820 genotype 8, 9
D7S820
alleles
Allele
frequency
7 repeats .0164
8 repeats .1655
9 repeats .1216
10 repeats .2949
Table 1. Frequencies for
select D7S820 alleles
National Institute of Standards
and Technology. "1036 Revised
U.S. Population" July 2017.
Dataset. https://strbase.nist.
gov/NISTpop.htm. Accessed
7/29/2020.
Forensic scientists use the frequency of each STR allele to determine
the frequency of each STR genotype using the formulas below:
For genotypes with two copies of the same allele
(ex: "5, 5" or "11, 11")
genotype frequency = p
2
where p = the frequency of the allele
For genotypes with different alleles (ex: "13, 14" or "6, 12")
genotype frequency = 2pq
p = the frequency of 1st allele
q = the frequency of the 2nd allele
