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STR Sequence Analysis for Characterizing Normal, Variant, and Null Alleles

NCJ Number
Forensic Science International: Genetics Volume: 5 Issue: 4 Dated: August 2011 Pages: 329-332
Date Published
August 2011
4 pages

This article discusses the system developed by scientists at the National Institute of Standards and Technology for providing short tandem repeat allele sequence analysis.


DNA sequence variation is known to exist in and around the repeat region of short tandem repeat (STR) loci used in human identity testing. While the vast majority of STR alleles measured in forensic DNA laboratories worldwide type as "normal" alleles compared with STR kit allelic ladders, a number of variant alleles have been reported. In addition, a sequence difference at a polymerase chain reaction (PCR) primer binding site in the DNA template can cause allele drop-out (i.e., a "null" or "silent" allele) with one set of primers and not with another. Our group at the National Institute of Standards and Technology (NIST) has been sequencing variant and null alleles supplied by forensic labs and cataloging this information on the NIST STRBase Web site for the past decade. The PCR primer sequences and strategy used for our STR allele sequencing work involving 23 autosomal STRs and 17 Y-chromosome STRs are described along with the results from 111 variant and 17 null alleles. (Published Abstract)

Date Published: August 1, 2011