The Paradyme™ 27GY STR System is Promega’s fourth eight-color STR chemistry kit. The system includes 23 autosomal STR loci (including CODIS markers); the Y-STR loci DYS391, DYS570, and DYS576; the internal quality indicators QIS and QIL; and the gender marker Amelogenin and is designed for use on the Spectrum CE System¹ and Spectrum Compact CE System².

It contains a reduced-stutter polymerase that produces cleaner STR profiles by lowering stutter peaks, making low-level minor contributor alleles easier to see and interpretation more consistent with fewer stutter-overlap borderline calls.

Because the system uses shorter amplicons with all 20 expanded CODIS core loci below

375 bp—it increases the likelihood of generating informative profiles from degraded samples.

Paradyme™ 27GY STR System also contains two quality indicators, QIS and QIL, that provide context about amplification performance across samples. In practice, QIS/QIL peak height ratios can help differentiate scenarios such as globally reduced amplification due to inhibition, locus dropout patterns consistent with degradation, or low signal due to limited template. This can support more consistent decisions about reprocessing (e.g., additional cleanup, re-amplification, alternate input strategies) and improve communication about sample limitations.

Figure 2: 0.5 ng of 2800M was amplified for 30 cycles with the Prototype reagents of Paradyme™ 27GY STR System. The amplified fragments were electrophoresed on the 8 capillary Spectrum CE instrument using 2 kV/18 sec injection and data was analyzed at 150 RFU AT (Analytical Threshold) using GeneMarker® HID Software for Spectrum CE Systems³.

Mixture interpretation is where many labs spend disproportionate time—especially when the minor contributor is low-level or the contributor ratio is highly imbalanced. Under these conditions, stutter becomes more than a predictable artifact; it becomes a competing explanation for peaks near allele positions.

Reducing stutter at the chemistry level can improve mixture interpretation by simplifying the peak landscape that drives probabilistic genotyping models and the human review that accompanies them offering:

» Cleaner inputs for probabilistic methods: fewer artifact peaks competing with allele hypotheses

» More consistent analyst experience: reduced dependence on subjective judgment for borderline peaks

This can make the probabilistic genotyping more powerful as the likelihood ratios obtained for genotypes for minor contributors are likely to be higher than they would be if the same sample had been processed with stutter.

In Figure 3, an example at D8S1179 locus illustrates reduced stutter artifact peaks in a mock mixture when comparing a conventional STR chemistry to Paradyme™ 27GY STR System.

Shown is the D8S1179 locus from a mock casework mixture amplified with PowerPlex® Fusion 6C System4 (left) and Paradyme™ 27GY STR System (right). In conventional STR chemistries, stutter is not always removed by a stutter filter—for example, elevated stutter artifacts due to coincident plus and minus stutter can elevate a stutter peak above the locus-specific threshold (allele 13 in Figure 3), causing it to be treated as an allele during mixture deconvolution (false-

positive allele). Conversely, a true minor-contributor allele (allele 15 in Figure 3) may fall below the stutter threshold, leading to its inappropriate exclusion from deconvolution (false-negative allele). Reducing stutter can lessen both failure modes and support clearer allele calling.