Individuals with a secondary education should have a knowledge level sufficient to make sense of what they read or hear about genetics, and they should be able to think scientifically in evaluation and decision-making processes. The purpose of this study is to identify the basic understanding of secondary education students about genetic concepts and the reasons for the difficulty of learning and teaching genetics. Semi-structured interviews that include student drawings have been conducted with 24 students to gain a comprehensive perspective on secondary education students' understanding of the basic concepts of genetics. The answers given by the students to the interview questions and their drawings have been analyzed with content analysis. Qualitative data analyzed with a holistic point of view were collected and evaluated under the categories of 'DNA, gene and chromosome' and 'Cell divisions and heredity relationship.' As a general result, it has been found that students have inaccurate and inconsistent information about the basic concepts of genetics, have difficulties in establishing relationships between these concepts, and cannot fully understand and explain the processes underlying genetic events. It has been observed that various factors have an effect on this result. It will be possible to support students to develop a more accurate understanding of genetic concepts and issues by working on the weaknesses in genetics teaching, providing an enriched teaching environment with current teaching methods and materials, and moving away from rote learning.