This paper presents the results of part of an investigation carried out with fourth-level Spanish secondary education students (15 years old), in which we implemented a teaching unit based on problem-solving methodology as an investigation to teach genetics and human inheritance curricular contents. By solving open problems, the students experienced a conceptual restructuring that stayed with them over time and involved the following specific theories: the location of hereditary information, the transmission of hereditary information, and the appearance of new characteristic. The learning connections between these specific theories were also studied. Furthermore, these results were compared with a control group that worked with closed problems, the usual approach to genetics teaching in Spanish classrooms. Consequently, we were able to verify that our methodology results in better learning.