Paternity Investigations Based on DNA-Analysis Only
Innumerable investigations have shown that conventional blood group typing is a powerful and reliable means to solve cases of disputed paternity in simple trio cases as well as in some of the more complicated deficiency cases. The benefit of the introduction of additional systems and of the sophistication of methods, e.g. isoelectric focusing was a constant increase of the so-called positive proof of fatherhood, but the chance to find a case not already showing exclusions in other systems remained extremely small. Inherently, the plethora of methods and systems also increased almost unnoticed the chance of error. Furthermore, the training time of new technical staff considerably lengthened. The appearance of the highly polymorphic DNA systems (Jeffreys et al., 1985, Smith et al., 1990) quickly unsecured a typing system that seemed to be well established forever. Bär (1988) compared the results and the practical handling of the so-called multi-locus probes in paternity investigations as well as in stain analysis. Many reasons, e.g. the poor statistical evaluation of the results of multi-locus probes and the delicate working conditions of low stringency showed that in the hands of ordinary technical staff the work with single locus probes gives more reproducible results. Furthermore, well known and accepted statistical approaches like the one of Essen-Möller or the calculation of a paternity index are possible. The easiness of the statistical combination of DNA results with those of conventional techniques is an additional strong argument for the use of single locus probes, not unimportant in difficult cases of severe deficiency(Bär and Hummel, 1991). Based on the results of many supplementary expertises in paternity cases showing low values of probabilities, single exclusions and opposite homozygosities after conventional blood grouping, we decided in March of 1991 to completely abandon the conventional systems and to exclusively use DNA single locus probes.
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