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
Table 1 below shows the allele frequencies for four D7S820 alleles.
Table 1
D7S820 alleles Allele frequency
7 repeats 0.0164
8 repeats 0.1655
9 repeats 0.1216
10 repeats 0.2949
2. Use the information in Table 1 to calculate genotype frequencies using the
formulas above. Show your work.
a. D7S820 genotype 7, 7
Type your answer here.
b. D7S820 genotype 7, 9
Type your answer here.
c. D7S820 genotype 10, 10
Type your answer here.
d. D7S820 genotype 8, 9
Type your answer here.
Electrophoresis Forensics Lab: Wrongfully Convicted? Student E-worksheet™.
Release: September 2023. © 2023 by miniPCR bio
TM
