Tri-Allelic Patterns

Three-banded or tri-allelic patterns are sometimes observed at a single locus in a multiplex STR profile. These tables of tri-allelic patterns are for scientists to "compare notes" as well as to see if certain allele combinations are more likely. Tri-allelic patterns generally fall into one of two different groups based on relative peak heights:


Type 1: Sum of heights of two of the peaks is equal to the third

Type 2: Balanced peak heights

We welcome your contributions in order to more fully catalog the genetic variation observed in these STR loci.

To contribute to these tri-allelic variant reports, click here.

388 total patterns reported as of 11/09/2015

[click on loci listed below for details]

Core STR Loci (263)


         CSF1PO (8)

         FGA (40)

         TH01 (4)

         TPOX (19)

         VWA (24)

         D3S1358 (11)

         D5S818 (8)

         D7S820 (20)

         D8S1179 (21)

         D13S317 (15)

         D16S539 (13)

         D18S51 (43)

         D21S11 (27)






Other Common STR Loci (61)


         D2S1338 (9)

         D19S433 (12)

         Penta D (12)

         Penta E (15)


         FES/FPS (1)



         SE33 (4)

          D10S1248 (2)

          D12S391 (2)

          D22S1045 (1)

          D1S1656 (3)






Y-STR Loci (64)

duplications or triplications

         DYS19 (8)

         DYS389I (4)

         DYS389II (6)

         DYS390 (1)

         DYS391 (3)


         DYS393 (2)

         DYS385 a/b (19)

         DYS438 (4)

         DYS439 (5)

         DYS437 (2)

         DYS448 (3)

         DYS456 (2)

         DYS458 (3)

         DYS635 (1)

         Y-GATA-H4 (1)


Variant Alleles

Information on Variant STR Alleles Sequenced at NIST

Some useful references with more information on tri-allelic patterns include:

Crouse et al. (1999) Analysis and interpretation of short tandem repeat microvariants and three banded allele patterns using multiple allele detection systems [published erratum appears in J. Forensic Sci. 1999 May;44(3)].  J. Forensic Sci. 44(1):87-94. They report finding 18 TPOX three-banded patterns, and one CSF1PO three-banded pattern.

Clayton et al. (2004) A genetic basis for anomalous band patterns encountered during DNA STR profiling. J Forensic Sci. 49(6):1207-1214.  They introduce the "Type 1" and "Type 2" nomenclature for tri-allelic patterns.

Butler, J.M. (2006) Genetics and genomics of core STR loci used in human identity testing. J. Forensic Sci. 51(2): 253-265.



Last Updated: 11/09/2015