Highlights
- •A sequence simplification strategy was introduced.
- •More stutter variants—including N-4, N-3, N-2, N0, N + 1, and N + 2—were studied.
- •One-repeat-unit-longer stutters (or PAs) were better predictors for backward stutters.
- •Co-stuttering patterns were observed between two adjacent continuous motifs.
Abstract
Despite improvements in characterizing stutters of short tandem repeats (STRs), the
relationships among the amounts of stutter variants and the relationships among motifs
are not well understood yet. In the present study, 750 peripheral blood samples from
human subjects were included to characterize the stutters of 58 STRs via the ForenSeq
DNA Signature Prep Kit on a MiSeq FGx instrument. Alleles and corresponding stutter
products were identified with a sequence simplification procedure. After screening,
26,921 alleles were included, that resulted in over 50 million reads, among which
8.69% were stutter products. Among these stutter products, 83.44% were N-1 stutters.
Additionally, N-4, N-3, N-2, N0, N + 1, and N + 2 variants accounted for 0.11%, 0.77%,
6.45%, 3.01%, 5.95%, and 0.25% of the stutter products, respectively. For backward
stutters, stutter products correlated best with the corresponding one-unit-longer
stutter (or parental allele), which may represent a good predictor for backward stutters.
For forward stutters, the N + 2 stutter correlated best with the N + 1 stutter, whereas
the N + 1 stutter correlated best with the N-1 stutter rather than the expected parental
allele, which indicated that the patterns were more complex for forward stutters.
Additionally, some interesting findings were obtained for D21S11. For two adjacent
contiguous motifs, co-stuttering patterns were observed where one motif tended to
increase one repeat unit while the other motif decreased one repeat unit, whereas
the inter-motif dependency was not significant for interrupted motifs. In conclusion,
with massively parallel sequencing technology and our sequence simplification strategy,
sequence variations within alleles and stutter products were identified, which was
useful to determine the origin of stutters, identify more stutter variants, and explore
the relationships among motifs. These findings may be helpful for allele designation,
a deeper understanding of the mechanism of stutter, and improving resolution in forensic
mixture analyses.
Keywords
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Article info
Publication history
Published online: December 09, 2019
Accepted:
December 8,
2019
Received in revised form:
November 19,
2019
Received:
April 8,
2019
Identification
Copyright
© 2019 Elsevier B.V. All rights reserved.
