Lee S. Tuckwiller, PhD, Uwe Heine, PhD, Marcia Eisenberg, PhD, George C. Maha, JD, PhD,
Karl-Hans Wurzinger, PhD, Ronald C. Barwick, PhD, Ruth P. Koester, PhD, Gary M.
Stuhlmiller, PhD, Lloyd C. Osborne, PhD, Clifton R. Harris, PhD, Tom Barrett, MS and James
M. Mason, PhD
Department of Paternity Evaluation, Laboratory Corporation of America Holdings,
Burlington, NC
Paternity testing results for CYP19 were examined for instances of maternal exclusion where the mother and child were apparently homozygous for different alleles. All such instances were observed in African Americans, and the incidence of null alleles in this population was estimated to be approximately 5% in the original study group. A subsequent study of a much larger sample indicated that the true incidence of apparent null alleles in this population is probably considerably lower. Interestingly, the null allele appears to be more common in mothers (1.4%) than alleged fathers (0.7%). Apparent null alleles have subsequently been observed in Caucasians, but with an incidence much lower than in the African-American population.
Cases of apparent null alleles were also observed in evaluating D17S5 PCR results. However, in six of these, a very large allele was demonstrated using a product specific probe, and thus they were actually instances of "allele dropout". In our experience with D17S5, it seems likely that most, if not all, apparent null alleles in this system result from the passage of a large, univisualized allele from parent to child.
If the incidence of apparent null alleles (whether due to "allele dropout" or a true null allele) is sufficiently high, their unaccounted for presence may result in a deviation from Hardy-Weinberg expectations.
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