Genetics can be a difficult topic to teach and learn in a traditional classroom. The objective of this qualitative classroom action research was to examine the effectiveness of a blend of problem-based learning (PBL) with scientific argumentation to improve student understanding of basic genetics. The research participants were grade 9 Bhutanese students accustomed to rote learning placed in small groups to competitively achieve a solution utilizing PBL and scientific argumentation. The six-week teaching intervention process was teacher evaluated daily and at the end of each unit followed by strategy and lesson adjustments by applying the cycles of action research: planning, acting, observing, and reflecting while considering the pre- and post-genetic tests, lesson plans, semi-structured observations, pre- and post-semi structured interviews, reflective journals, and, student learning tasks. Content analysis and method triangulation were used to confirm that the blending approach was effective in helping students to acquire basic knowledge and to eliminate most misconceptions about five central subtopics in the study of genetics: inheritance, variation, genetic engineering, cloning and evolution. An assessment of teacher journals and outsider evaluations of teacher lessons and presentations revealed an increasing teacher appreciation for the blended method. This intervention helped students become independent and active learners.