A Tcl/Tk graphical user interface for simple DNA mixtures resolution using allele peak heights or areas information when two alleles are observed at a given locus


The A2.simu function launches a Tcl/Tk graphical interface with functionalities devoted to two-person DNA mixtures resolution, when two alleles are observed at a given locus.




When two alleles are observed at a given locus in the DNA stain, seven genotype combinations are possible for the two contributors: (AA,AB), (AB,AB), (AA,BB), (AB,AA), (BB,AA), (AB,BB) and (BB,AB), where A and B are the two observed alleles (in ascending order of molecular weight). Having previously obtained an estimation for the mixture proportion, it is possible to reduce the number of possible genotype combinations by keeping those only supported by the observed data. This is achieved by computing the sum of square differences between the expected allelic ratio and the observed allelic ratio, for all possible mixture combinations. The likelihood of peak heights (or areas), given the combination of genotypes, is high if the residuals are low. Genotype combinations are thus selected according to the peak heights with the highest likelihoods.

The A2.simu() function launches a dialog window with three buttons:
-Plot simulations: plot of the residuals of each possible genotype combination for varying values of the mixture proportion across the interval [0.1, 0.9]. The observed mixture proportion is also reported on the plot.
-Simulation details: a matrix containing the simulation results. Simulation details and genotype combinations with the lowest residuals can be saved as a text file by clicking the “Save" button. It is also possible to choose specific paths and names for the save files.
-Genotypes filter: a matrix giving the mixture proportion conditional on the genotype combination. This conditional mixture proportion helps filter the most plausible genotypes among the seven possible combinations. The matrix can be saved as a text file by clicking the “Save" button. It is also possible to choose a specific path and a name for the save file.


-Linux users may have to download the libtktable package to their system before using the A2.simu function. This is due to the Tktable widget, used in forensim, which is not (always) downloaded with the Tcl/Tk package.
-For the computational details, please see forensim tutorial at http://forensim.r-forge.r-project.org/misc/forensim-tutorial.pdf.


Hinda Haned h.haned@nfi.minvenj.nl


Gill P, Sparkes P, Pinchin R, Clayton, Whitaker J, Buckleton J. Interpreting simple STR mixtures using allele peak areas. Forensic Sci Int 1998;91:41-53.

See Also

A3.simu: the three-allele model, and A4.simu: the four-allele model



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