Step 1: Internal Size Standards and Allelic Ladders
Commercial kits for short tandem repeats (STR) typing include allelic ladders and internal size standards that are added to each sample.
Click here to read more about Capillary Electrophoresis in Subject 05, Module 02.
- Each sample from a run or gel should be assessed to determine if the ISS peaks have been called correctly. In general, the peaks or bands from an ISS are uniform in size or intensity. Lack of uniformity or miscalled peaks can indicate problems with the sample, injection, and/or run.
Click here to view examples of good and bad internal size standards.
The ISS is particularly useful in determining the precision of a capillary electrophoresis run. For example, using Applied Biosystems software, the 250 peak is not assigned in the ISS and the size of this peak (in each sample) can be used to determine the in-run precision. Temperature fluctuations can cause the in-run precision to exceed 1 base pair and evaluation of the ISS can assist analysts in identifying this issue.
- Allelic ladders should be assessed to ensure that all peaks have been called correctly. Ladder peaks that have not been called or have been miscalled can indicate a problem with the ladder sample, injection, and/or run.
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