U.S. flag

An official website of the United States government, Department of Justice.

Democrats have shut down the government. Department of Justice websites are not currently regularly updated. Please refer to the Department of Justice’s contingency plan for more information.

STR Data Analysis and Interpretation for Forensic Analysts

Null Alleles

Home  |  Glossary  |  Resources  |  Help  |  Contact Us  |  Course Map
 

A null allele is an allele that is present in a sample, yet is not amplified. A primer-binding site mutation can inhibit amplification for that allele and result in a null allele. If an individual is heterozygous and has a primer-binding site mutation for one of the alleles, the individual would type as a homozygote.

Note:

The manufacturers of various STR typing kits use different primer sets. If a DNA sample has a mutation in a primer-binding region specific to kit A, but no mutation in the primer-binding region specific to kit B, a rare discordance in allele calls can occur when comparing typing results produced by these two manufacturers' kits.07

When comparing DNA typing results from different kits, null alleles (due to primer-binding site mutations) can result in discrepant DNA types at a particular locus. It is important to understand that although null alleles are rare, they must be considered when interpreting potential matches.

Back Forward