Example of Percent Contribution

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Example of Percent Contribution

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Consider the evaluation of the following:

FGA
Allele	Peak Height
19*	250
20	674
23	717
25*	225
* Visual minor alleles

There appears to be a major and a minor contributor. Assuming only two donors, the mixture proportions are estimated by summing the peak heights of the two major or minor alleles and dividing by the peak heights of all four alleles. This is then multiplied by 100 to provide a percentage contribution.

250 + 225 / 250 + 674 + 717 + 225 = .25 x 100 = 25% contribution from the minor donor
674 + 717 / 250 + 674 + 717 + 225 = .75 x 100 = 75% contribution from the major donor

This can also be represented as a ratio by summing the peak heights of the two minor alleles and dividing them by the sum of the peak heights from the two major alleles.

250 + 225 / 674 + 717 = .34 or a ratio of approximately 1 to 3

A second check of this hypothesis is evaluation of the peak height percentages. In this case the peak height percentage for genotype 1 (19, 25) is 90% and genotype 2 (20, 23) is 94%. These values are within the acceptable range of peak height percentage for balanced heterozygotes.

This evaluation can be done at any locus with no shared alleles to estimate the proportion from each contributor. Once the estimate is established, loci with two or three alleles can be evaluated.

Note:

Genotype #1	Genotype #2
A,B	C,D
A,C	B,D
A,D	B,C
C,D	A,B
B,D	A,C
B,C	A,D

In some cases major/minor contributors cannot be established, the calculations noted above can be performed for each combination to determine the percent contribution from each donor.

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