22 How a Flower Gets Its Color-Mid

How a Flower Gets Its Color FOCUS Question How do plants get their traits?

Growing a Garden Suppose you have a garden full of bright red marigolds. One day, you spot a single white marigold among all the red ones. The two colors look nice together, and you think a mix of red and white flowers would make a beautiful garden. You know that each flower will produce seeds, which can grow into new marigolds. To get more white flowers, you decide to plant the seeds that grow inside the white flower. But you soon discover that your simple plan wasn't so simple.

What Are Traits? Flower color is one way to describe marigolds. It is a trait— a characteristic of a living thing. Other traits of marigolds include spiky leaves and many small stems. They grow to a height of about 30 centimeters (12 in.). All plants have traits. For example, oak trees have broad leaves and a wooden trunk and grow to a height of about 25 meters (82 ft.). All marigolds have similar traits to one another. However, each marigold may have slightly different traits. One marigold may have white flowers. Another may have red flowers. Every cell in every living thing has a set of instructions for growing its traits. The instructions are found inside a chemical code called DNA.

Living things get DNA from each parent. You got half of your DNA from your mother and half from your father. The two sets of DNA then combined, and you received some traits from each parent. Every living thing's traits are inherited, which means they come from its parents' DNA. Plants combine DNA when pollen from one plant reaches the flower of another plant. The flower makes seeds, which grow into new plants. The seeds from your white marigold got half of their DNA from the white flower and half from the pollen of one of the red marigolds. What color will the new flowers be? Do You Know? Some traits are a blend of both parents' traits. Other traits are affected by the environment. For example, an oak tree in a dry area will not grow very tall, even if it has a "tall" trait in its DNA.

Not So Simple You plant the seeds from the white marigold in a big pot, and eight plants spring up. You predicted that half would have red flowers and half would have white flowers. Or maybe all eight flowers would be pink since red and white make pink. When the flowers open, you can't believe it. All eight flowers are red! Instead of planting the new flowers in the garden, you leave them in the pot. In time, they produce new seeds, but you ignore them. Their flowers will just be red anyway, right?

A few months later, you check the pot of marigolds again. The eight red plants have wilted, but there are twelve new plants. Nine are red and three are white! What's going on? You still want white flowers, so you carefully transfer pollen from the stamen of one white flower onto the pistil of another white flower. Soon, seeds develop from the two parents that had white flowers. When these new plants grow. all the flowers are white. You're happy, but this makes no sense! Or does it?