What is a DNA degradation index and how is it used?

• A. A ratio comparing short to long DNA targets to assess sample quality and predict amplification success.
• B. A ratio of male to female DNA.
• C. A measure of total DNA concentration.
• D. A ratio comparing long to short DNA targets to assess sample quality and predict amplification success.

Answer: (D)

The main idea being tested is how DNA integrity is quantified with a degradation index. This index is a ratio derived from measuring a long DNA target and a short DNA target from the same sample. Because longer fragments break down more readily, degraded DNA shows a lower amount of the long target relative to the short one, lowering the ratio. This makes the degradation index a useful assess­ment of sample quality and a predictor of how well longer loci will amplify in a multiplex STR analysis. A high long-to-short ratio suggests the DNA is relatively intact and longer loci are likely to amplify, while a low ratio points to substantial degradation and often leads to choosing shorter, mini-amplicon targets or re-extraction. The key takeaway is that the degradation index uses the long-to-short ratio to gauge DNA quality, not total DNA quantity or gender.