Diane Daigle, age 13, of Deer River, Minnesota, for her question:
How can a seed make a plant have certain colors?
Every plant, of course, is descended from a long line of assorted ancestors. Life is handed down from generation to generation. The life of a plant may be handed on in a seed. With the gift of life, the seed also carries a set of instructions about features inherited from its family tree.
The color scheme of a plant is caused by pigment molecules made from simple chemicals such as carbon and hydrogen. We see them as colors because they just happen to trigger the human vision in certain ways. To the plant, they are merely chemicals with special duties to perform. But the colorful beauty of the plant world prodded human curiosity to probe the mysteries of heredity and helped lead to our present understanding of inherited family features in plants and animals and also in people.
In the 1800s, Gregor Mendel was curious about color variation in generations of his garden pea plants. Patient notes, careful records and lots of sound reasoning led him to the answer. And the answer uncovered a basic law of nature. Mendel used it to predict that seeds from one red and one white parent would all produce red flowers. In the next genera¬tion of the same family, there would be three red flowers to one white. The dominant red characteristic appeared most often. The less dominant white feature was hidden until allowed to appear in a few offspring. Mendel proved that family features are inherited according to a definite ratio.
Later scientists learned Mendel's law and delved for still deeper answers to heredity. They found answers in the genes and chromosomes of living cells. Molecular biologists . probed even deeper into the chemicals from which these genes are made. And there they found a set of instructions that decides the make up and the activities of every living cell. This complex chemical is called DNA. It orders the manufacture of the pigments that color the leaves and stems, the flowers and seeds of each living plant.
Each seed has a quota of DNA inherited from the family tree. It tells the seed just how and when to sprout. The nucleus of each new cell has a copy of the original blueprint in the seed. The DNA instructs the marigold to paint her face with yellow or vivid orange. It tells the geranium to use flower colors of pale or vivid tones of red. It tells a pine tree to make lots of green green chlorophyll molecules. It orders the oak to make yellow¬ colored chemicals as well as the green chlorophyll. In the fall, when the green chemicals depart, we see the yellow chemicals unmasked and the oak is dressed in golden glory.
Mankind's inherited curiosity leads us to probe into the nature of the human body. Its miracles and misfortunes, its strengths and weaknesses are inherited from long lines of human ancestors. The more we know of these inherited characteristics, the better. Modern science is on the verge of assembling living cells from non living chemicals. Gregor Mendel's pea sorting led to a major breakthrough in biology. He would have felt humbly proud that he had advanced a step toward mankind's ultimate understanding of the body he is born to inherit.