One year variability of peak heights, heterozygous balance and inter-locus balance for the DNA positive control of AmpFℓℓSTR© Identifiler© STR kit

Multivariate analyses of 205 positive control experiments in an AmpFℓℓSTR© Identifiler© STR kit were used to analyze the factors affecting peak heights at 16 loci. Peak heights were found to be highly correlated between loci and there was evidence for a difference in sensitivity of the two genetic analyzers in the blue channel. Heterozygous balance response at 10 loci was found to behave as a random variable following a beta-distribution with typical median values of 90%, without locus or genetic analyzer effect. Inter-locus balance at 16 loci was influenced by the blue channel effect and a temporal switch of unexplained origin. The implications of these results for the choice of minimum threshold values in quality control are discussed.