Exams constitute the predominant form of summative assessment in undergraduate biology education, with the assumption that exam performance should reflect student conceptual understanding. Previous work highlights multiple examples in which students can answer exam problems correctly without the corresponding conceptual understanding. This disconnect can significantly undermine instructors' ability to interpret exam performance in relation to student learning. Here, we investigate problem-solving strategies used by undergraduate students in biological sciences. Participants were interviewed using a semi-structured protocol: They were asked to solve genetics problems, in multiple-choice and short-answer formats, and were prompted to explain their strategies. Data analysis took a grounded-theory approach and involved iterative close reading of the interview transcripts to examine students problem-solving strategies. Three case studies of participants with similar overall exam performance are presented to explore the variety of strategies. We identified two non-conceptual strategies based on algorithms or patterns within the exam problems. In contrast, the third case-study participant used mostly conceptual strategies grounded in an understanding of biology. We also observed participants switching between conceptual and non-conceptual strategies. These results identify different strategies that undergraduate students use to solve problems in biological sciences, and potential implications on the design of exams and assessments are discussed.