TED-Ed

View full lesson: http://ed.ted.com/lessons/secrets-of-the-x-chromosome-robin-ball The sequence of DNA that we inherit from our parents encodes directions for making our cells and giving us specific traits. Identical twins have the same DNA sequence, so how can one twin end up with a genetic disorder while the other twin does not? Robin Ball explains how the secret lies in X chromosome inactivation. Lesson by Robin Ball, animation by Anton Trofimov.