U.S. flag

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

STR Data Analysis and Interpretation for Forensic Analysts


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

Electropherograms demonstrating pull-up
National Institute of Justice (NIJ) (see reuse policy).

Pull-up, sometimes referred to as bleed-through, represents a failure of the analysis software to discriminate between the different dye colors used during the generation of the data. Oversaturated data can also cause the dyes to "bleed" over or pullup into another color.

If pull-up occurs, the analyst can inject less of the sample or re-amplify the sample with less input DNA. Reoccurring pull-up (due to too much DNA) may indicate that the quantitation method or the amount of DNA used for amplification should be reevaluated. If this problem is not due to too much DNA, it may be necessary to run a new matrix and apply it to the sample.

A signal from a locus labeled with blue dye, for example, might mistakenly be interpreted as a yellow or green signal, thereby creating false peaks at the yellow or green loci. Pull-up can usually be identified through careful analysis of the position of peaks across the color spectrum, but there is a danger that pull-up will go unrecognized, particularly when the result it produces is consistent with what the analyst expected or wanted to find.

Back Forward