Various sequences for teaching genetics have been proposed. Three seventh-grade biology textbooks in Taiwan share similar key knowledge assemblages but have different knowledge arrangements. To investigate the influence of knowledge arrangements on student understanding of genetics, we compared students' reading comprehension of the three texts that exhibit different knowledge arrangements. The results revealed that one particular knowledge arrangement (genetic materials, mitotic and meiotic models, genetic model, and molecular model) leads to the greatest reading comprehension of genetics. The differences are found in knowledge of mitotic and meiotic models. The results of this study are valuable for use in organizing instruction.