The doorbell rings. Emma's dad calls out, "Emma, answer the door! I'm making dinner and my hands are full!"
Emma puts down her book, and heads to the door. As she opens it slowly, a burst of mostly familiar faces rush through the door. Aunts, uncles, and cousins she hasn't seen in years greet her enthusiastically.
Aunt Rita pulls Emma into a hug and says, "Well, look at you! You've grown! And you've got such beautiful red, curly hair! It runs in the family, you know. You look just like my grandmother!"
Uncle Michael adds, "And, look, she's getting so tall! Just like her dad. Only 10 years old, and you look like a basketball player already!"
Emma's dad emerges from the kitchen to greet the guests. As he helps everyone get settled, Emma wonders, "Aunt Rita's grandmother? It runs in the family? What are they talking about?"
Genes (say: jeenz), that's what they're talking about. Genes play an important role in determining physical traits - how we look -and lots of other stuff about us. They carry information that makes you who you are and what you look like: curly or straight hair, long or short legs, even how you might smile or laugh. Many of these things are passed from one generation to the next in a family by genes.