Paternity exclusion by DNA markers: effects of paternal mutations

In parentage testing when one parent is excluded, the distribution of the number of loci showing exclusion due to mutations of the transmitting alleles is derived, and it is contrasted with the expected distribution when the exclusion is caused by nonpaternity. This theory is applied to allele frequency data on short tandem repeat loci scored by PCR analysis, and VNTR data scored by Southern blot RFLP analysis that are commonly used in paternity analysis. For such hypervariable loci, wrongly accused males should generally be excluded based two or more loci, while a true father is unlikely to be excluded based on multiple loci due to mutations of paternal alleles. Thus, when these DNA markers are used for parentage analysis, the decision to infer non-paternity based on exclusions at two or more loci has a statistical support. Our approach places a reduced weight on the combined exclusion probability. Even with this reduced power of exclusion, the probability of exclusion based on combined tests on STR and VNTR loci is sufficiently large to resolve most paternity dispute cases in general populations.