In this module, students explore how mutations can affect proteins and traits. Students examine random, inherited, and environmental causes of mutations, focusing on substitution mutations and frameshift mutations caused by insertions and deletions. Students transcribe, translate, and mutate a DNA sequence to create and compare “mutant chickens,” visualizing how DNA changes can produce diffrences in traits. The module concludes with a medical case study in which students take the role of doctors, analyzing CFTR gene sequences to diagnose patients with cystic fibrosis. Students will learn that mutations can be positive, negative, or neutral and play an important role in genetic variation.