HIV protease variant frequencies versus MAPP score. (A) Frequency of each variant by position within the population of untreated individuals plotted against its MAPP score. Rare variants (frequency <0.1%) are in blue, common variants (frequency >5%) are in red, and those in between are in green. Variants known to confer resistance to protease inhibitors are the bordered squares; the remaining variants are circles. (B) Plot of variant frequency after treatment with protease inhibitor(s). Common variants with high MAPP scores are labeled and ranked by effectiveness in conferring resistance. Color-coding of variants is by their frequency in untreated patients, as in A, for comparison.