Each cell in the human body contains about 25,000 to 35,000 genes, which carry information that go toward determining your traits. Traits are characteristics you inherit from your parents; this means your parents pass some of their characteristics on to you through genes. For example, if both of your parents have green eyes, you might inherit the trait of green eyes from them. Or if your mom has freckles, you might inherit that trait and wind up with a freckled face. And genes aren't just in humans — all animals and plants have genes, too. Each father and mother pass down traits to their children, who inherit combinations of their dominant or recessive alleles. But how do we know so much about genetics today? Hortensia Jiménez Díaz explains how studying pea plants revealed why you may have blue eyes. From something as small and complex as a chromosome to something as seemingly simple as the weather, sex determination systems vary significantly across the animal kingdom. Biologist and teacher Aaron Reedy shows us the amazing differences between species when it comes to determination of gender. How can a “thumbs up” sign help us remember five processes that impact evolution? The story of the Five Fingers of Evolution gives us a clever way of understanding change in gene pools over time. What do a man, a mushroom, and an elephant have in common? A very long and simple double helix molecule makes us more similar and much more different than any other living thing. But, how does a simple molecule determine the form and function of so many different living things?

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