Genetic subjects must be followed by every student the education program of Biology STKIP PGRI Sumbar in the fifth semester. In sex-linked gene material, there are concepts, sub-materials, and exercises that are difficult for students to understand. This is due to the students\' habits that are only waiting for information from lecturers, students do not have independent study habits, and the unavailability student worksheet that can help student difficulties. This study aims to develop a practical student worksheet based on Mastery learning in sex-linked gene material. The type of research is 4-D modelsare defined, design, and development. In this research limited to development stage (practicality test) of student worksheet based on mastery learning in sex-linked gene material. Practicality test is done by the lecturer of genetic subjects and students. Based on the results of practical tests conducted by lecturer and students, the ease of use aspect shows practical criteria with 80% and 81.27%. Student worksheet based on mastery learning in sex-linked gene material is practically used for lecturers and students.