Genetics, an integral component of biological sciences, is important because it serves as a foundation for understanding inheritance, diversity, and evolution. it is difficult topic at secondary school and undergraduate Problem-solving in genetics is difficult because it requires strategic integration of complex knowledge including concepts , procedures , and models .This study investigates the problem –solving behaviors of secondary school students ( n = 80 ) when solving7 genetics problems. By using a questionnaire ,genetics problem – solving performance test developed by the researcher and holistic strategy ( key concepts of genetics and relationships , diagrams, and intensive exercises ). The results revealed differences between pre-post tests of experimental group in favor of post-test and the holistic strategy was important to develop problem-solving behaviors .