Genes, DNA, and You
TAKE a good, long look at yourself in the mirror. Note the color of your eyes, the texture of your hair, the shade of your complexion, and the shape of your body. Think about the talents that you possess. Why do you look the way you do? Why do you have the particular traits and talents that you do? Today the mystery is being clarified through an understanding of genetics—the study of heredity—and the effects of environment.
‘Genetics?’ you moan. ‘That subject sounds too scientific and too difficult to understand!’ However, have you ever told someone that she has her father’s green eyes but her mother’s red hair and freckles? If so, you already know a basic fact of genetics—physical traits are passed from parent to child. In addition, that fact may be the decisive start to your understanding how man got here—by evolution or by creation. To begin, let us see how each of us carries the heritage of many generations.
Your body is made up of tiny living units called cells—some 100 trillion of them, according to one estimate. Inside each cell, within its nucleus, there are thousands of genes. They are individual units of heredity that control the cell and therefore determine some of your characteristics. Many genes may order your blood type; others, your hair texture, your eye color, and so on. So each cell carries a miniature blueprint or codebook made up of genes, which contains all the instructions needed to build, repair, and run your body. (See diagram, page 5.) Could all of this have happened by accident?
How the Mystery Was Unraveled
The theory that traits were inherited through the blood was devised by Aristotle in the fourth century B.C.E. and was generally accepted for over a thousand years. This so affected the thinking of the day that in the English language, people speak of bloodlines and blood relatives.
In the 17th century, egg cells and sperm cells were discovered, but their actual role was misunderstood. Some thought that tiny, fully formed creatures were present in either the egg or the sperm. By the 18th century, though, researchers correctly recognized that an egg and a sperm combine to form an embryo. Nevertheless, an accurate explanation of heredity was still to come.
It wasn’t until 1866 that an Austrian monk named Gregor Mendel published the first correct theory of heredity. From his experiments with garden peas, Mendel discovered what he called “discrete hereditary elements” hidden in sex cells, and he asserted that these were responsible for the passing on of traits. These “discrete hereditary elements” we now call genes.
About the year 1910, genes were found to be located on cell structures called chromosomes. Chromosomes consist primarily of protein and DNA (deoxyribonucleic acid). Since scientists were already aware of the important role of proteins in other cell functions, they assumed for many years that chromosomal proteins carry genetic information. Then, in 1944, researchers presented the first proof that genes consist of DNA, not protein.
In 1953, when James Watson and Francis Crick discovered the chemical structure of DNA, coiled threadlike molecules, man’s unraveling of the mystery of life took a great step forward.