Two Person Mixture with Two Alleles at a Locus

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Two Person Mixture with Two Alleles at a Locus

Home > STR Data Analysis & Interpretation > Data Interpretation and Allele Calls > Example of Percent Contribution > Two Person Mixture with Two Alleles at a Locus

Consider the following information:

D5S818
Allele	Peak Height
9	794
11	1201

The same approach can be used to estimate the mixture percentages and interpret data in a two person mixture case with two alleles at a locus. This information can aid in determining the most likely genotypes of the major and minor contributors.

The following scenarios are possible:

Possible Scenarios
Scenario	Genotype #1 (Major)	Genotype #2 (Minor)
1	9,9	9,11
2	9,11	9,11
3	9,9	11,11
4	9,11	11,11
5	9,11	9,9
6	11,11	9,9
7	11,11	9,11

Scenario #1
This scenario is unlikely because a shared 9 allele would leave a very low percent contribution for Genotype #1.
Scenario #2
If it is assumed that the minor donor contributed 25% and the major donor contributed 75% (based on FGA results).

The estimated peak height percentage would be:
- Genotype #1 would be 198/300 x 100 = 66%
- Genotype #2 would be 596/901 x 100 = 66%
Scenario #3
The percent contribution would be:
- Genotype #1 (794 / 794 + 1201) x 100 = 40%
- Genotype #2 (1201 / 794 + 1201) x 100 = 60%
Scenario #4
In this scenario, 11 is a shared allele and it is assumed that the contribution is equal to that of the 9 allele which is 794 RFUs (Genotype #1). This would leave Genotype #2 contributing 407 RFUs.

The percent contribution would be:
- Genotype #1 = (794 + 794/ 794 + 1201) x 100 = 80%
- Genotype #2 = (407 / 794 + 1201) x 100 = 20%
Scenario #5
This scenario unlikely since a shared 9 allele would leave a very low percent contribution for Genotype #2.
Scenario #6
See scenario #3, as this is the reverse.

The percent contribution would be:
- Genotype #1 (1201 / 794 + 1201) x 100 = 60%
- Genotype #2 (794 / 794 + 1201) x 100 = 40%
Scenario #7
See scenario #4, as this is the reverse

In this scenario, 11 is a shared allele and it is assumed that the contribution is equal to that of the 9 allele which is 794 RFUs (Genotype #2). This would leave Genotype #1 contributing 407 RFUs.

The percent contribution would be:
- Genotype #1 = (407 / 794 + 1201) x 100 = 20%
- Genotype #2 = (794 + 794/ 794 + 1201) x 100 = 80%

Based on these seven scenarios:

Scenarios 2, 4, and 7 are possible
Scenarios 3 and 6 are less likely
Scenarios 1 and 5 are not likely

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