Highlights
- •We looked for tri-allelic subjects in 75,113 families.
- •The extra TPOX allele was the allele 10.
- •The tri-allelic pattern study has important consequences for forensic applications.
Abstract
Genotyping of polymorphic short tandem repeats (STRs) loci is widely used in forensic
DNA analysis. STR loci eventually present tri-allelic pattern as a genotyping irregularity
and, in that situation, the doubt about the tri-allele locus frequency calculation
can reduce the analysis strength. In the TPOX human STR locus, tri-allelic genotypes
have been reported with a widely varied frequency among human populations. We investigate
whether there is a single extra allele (the third allele) in the TPOX tri-allelic
pattern, what it is, and where it is, aiming to understand its genomic anatomy and
to propose the knowledge of this TPOX extra allele from genetic profile, thus preserving
the two standard TPOX alleles in forensic analyses. We looked for TPOX tri-allelic
subjects in 75,113 Brazilian families. Considering only the parental generation (mother + father) we had 150,226 unrelated subjects evaluated. From this total, we found 88
unrelated subjects with tri-allelic pattern in the TPOX locus (0.06%; 88/150,226).
Seventy three of these 88 subjects (73/88; 83%) had the Clayton's original Type 2
tri-allelic pattern (three peaks of even intensity). The remaining 17% (15/88) show
a new Type 2 derived category with heterozygote peak imbalance (one double dose peak
plus one regular sized peak). In this paper we present detailed data from 66 trios
(mother + father + child) with true biological relationships. In 39 of these families (39/66; 59%) the
extra TPOX allele was transmitted either from the mother or from the father to the
child. Evidences indicated the allele 10 as the extra TPOX allele, and it is on the
X chromosome. The present data, which support the previous Lane hypothesis, improve
the knowledge about tri-allelic pattern of TPOX CODIS’ locus allowing the use of TPOX
profile in forensic analyses even when with tri-allelic pattern. This evaluation is
now available for different forensic applications.
Keywords
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Article info
Publication history
Published online: November 26, 2014
Accepted:
November 19,
2014
Received in revised form:
October 24,
2014
Received:
September 24,
2013
Identification
Copyright
© 2014 Elsevier Ireland Ltd. Published by Elsevier Inc. All rights reserved.
