Abstract
4′,6-diamidino-2-phenylindole (DAPI)-stained visible nuclei counting has been shown to be an invaluable technique in the selection of hair samples for short tandem repeat (STR) typing. However, it is important to establish a threshold count of visible nuclei, which refers to the minimum number of visible DAPI-stained nuclei identified in a hair root required to produce an STR profile that meets minimum National DNA Index System (NDIS) upload eligibility requirements. In previous research, a robust threshold could not be established due to the scarcity of donor hair roots containing less than 100 visible nuclei. Therefore, this study revisits the previously established threshold of greater than or equal to 100 visible nuclei, while incorporating modifications in both the hair sample and DNA processing workflows to mirror casework practices. The results suggest that a minimum threshold of 25 visible nuclei is adequate to obtain STR profiles that are suitable for NDIS upload.
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