An STR electropherogram from a victim of sexual assault shows an XY pattern at the Amelogenin locus, but subsequent testing of the same male contributor reveals no amplification at any Y STR marker, and the Amelogenin Y band is again absent on repeat. The most likely technical explanation is:

• A Random allele dropout affecting only large amplicons
• B Somatic mosaicism limited to the sampled tissue
• C Contamination of the extract with female DNA masking the Y signal
• D A mutation deleting the Amelogenin Y specific region in this individual ✓

Explanation

Some males carry deletions spanning the Y segment of the Amelogenin gene used for sex typing, so they produce only the X sized product and may be misclassified as female at that marker. When Y STR markers also fail despite adequate input DNA and clean controls, a genuine AMELY deletion in the contributor is the accepted explanation rather than stochastic dropout, which is template dependent and inconsistent between repeats.

Reference: Butler, Forensic DNA Typing, 2nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.