Nowadays, there is a need in science education to consider scientific research and its applications alongside ethical consensus. Even though classroom debates of value issues have been demonstrated to significantly contribute to the raising of social consciousness and awareness, research shows that neither academics in higher education nor teachers in primary and secondary education deal with these issues sufficiently in their classes. In this study, the "Framework for Teaching Bioethics" was used in tackling the ethical issues about "Genetic Screening Tests" (GST) and "Genetically Modified Organisms" (GMOs). The present study examined the effect of "Framework for Teaching Bioethics" on students' argumentation quality and on students' ethical values which students consider while they are deciding about the ethical dilemmas. Also the contribution of individuals' content knowledge on the argumentation quality was examined. In this study a quasi-experimental pre-post test design was used. The participants of the study were biology teacher candidates (n = 38). "Achievement Test" ("AT") and "Bioethical Values Instrument" ("BVI") were used as data collection tools. Also interviews were conducted with 12 of participants, who were selected according to their AT scores. During interviews, participants advanced their positions about ethical dilemmas, which were about "genetically modified" organisms and genetic screening tests. Participants' arguments assessed in terms of justifications and their scientific grounds based on a four point rubric (Argumentation Quality Rubric). Results indicate that "Framework for Teaching Bioethics" significantly affected students' argumentation quality and content knowledge was not significant factor for prediction of argumentation quality.