An understanding of basic science is central to student success at the university level, even for students who will never work in scientific fields. Our investigation into students' understanding of DNA is part of a larger investigation into students' knowledge and attitudes about science. DNA and the concepts associated with it (e.g., heredity and genetic information) are necessary to interpret popular reports of biology, make health-care decisions, and to understand the spread and treatment of diseases in the world. In this research, we have built upon a previous study that looked at students enrolled in an introductory undergraduate astronomy course. The majority of these students are nonscience majors and are representative of the college-educated, general public. Unsurprisingly, the overall science knowledge scores of students who self-reported as science, technology, engineering, or mathematics (STEM) majors were higher than the scores of non-STEM majors. We have found that students arrive at college with reasonable levels of general science knowledge. However, a significant fraction seem unaware of two of the most profound insights of biology from the past few centuries: that species evolve and that DNA is the carrier of heritable information.