Below is an STR allelic series for many of the loci used in forensic STR analysi

ID: 174119 • Letter: B

Question

Below is an STR allelic series for many of the loci used in forensic STR analysis. For instance, for locus TPOX there are 8 different alleles in the human population and for D2S1338 there are 14 alleles in the human population. John Doe has the following profile: TPOX(7, 8), D7S820(10, 10), CSF1PO (7, 8), VWA (12, 14) and D3S1358(6, 6). What is the chance that you have the same STR profile as John does for these 4 STR loci? How many different gametes can John produce with respect to these 5 STR loci?

Explanation / Answer

To count the chance that we get the same STR profile is depend upon counting of allele frequencies. Allele frequencies is counted by (the people observable)/(total people). If we have allele frequencies we can easily count that for example:

Formula

CSF1PO 7=p, CSF1PO 8=q

0.19=p, 0.21 =q

2pq = 0.0798

TPOX 7(p), 8(q)

0.25=p, 0.31=q

2pq= 0.16

VWA 12, 14

0.015 =p, 0.1311=q

2pq = 0.003933

Then count all the frequencies = 0.0798+0.16+0.003933=0.3178 or 3178/10000= 1/3.14

Every three people the STR profile will common. [for an example, but it doesn’t happen]