This animation is made to introduce pre-medical and higher-level college students majoring biology to genetics by explaining X inactivation. Most educational resources are too conceptual or too technical to teach the concept and mechanism at the same time. In this animation, a calico cat, the most visible example of x inactivation, is used as the main character to tell the story in a more engaging way. A 2D animation technique is used to explain the conceptual information, while 3D techniques are used to explain in depth information of the molecular scenes.