You are sitting in a dark movie theater. You are trying to enjoy the movie, but you keep thinking about a pesky piece of popcorn stuck between your molars, the back teeth. After fumbling for a toothpick in your pocket, you dislodge the popcorn. You glance down at the toothpick and see a bit of blood from your gums. Although the popcorn is gone, your tooth still throbs with pain.

Your DNA is unique, and it makes you a human, not any other animal. Sequencing DNA lets us identify genetic similarities and differences that relate to species similarities and differences.