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.
Peering Into the Microscope
THE cell has been called the fundamental unit of life. Indeed, living things—including plants, insects, animals, and humans—are made up of cells. Over the years, scientists have peered into the inner workings of the cell and have unlocked many of the secrets of molecular biology and genetics. Let us take a closer look at cells and consider what science has discovered about these fascinating microscopic units of life.A Peek at the Microscopic
Cells vary in shape. Some are rectangular; others are square. There are round cells, egg-shaped cells, and some that simply look like blobs. Consider the amoeba, a one-celled organism that has no defined shape at all. Instead, it changes its form as it moves. Interestingly, the function of a cell is often suggested by its shape. For example, some muscle cells are long and thin and contract as they perform their work. Nerve cells—which relay messages throughout the body—have long branches.Cells also differ in size. Most, though, are too small to be seen by the naked eye. To illustrate the size of an average cell, look at the period at the end of this sentence. About 500 average-size cells could fit within that little dot! If that seems tiny, consider that some bacterial cells are about 50 times smaller. The largest cell? That designation belongs to the yolk of an ostrich egg—a one-celled “giant,” which is about the size of a baseball or a cricket ball!
Since most cells cannot be seen with the naked eye, scientists employ instruments, such as the microscope, to study them. Even then, some intricate details of a cell cannot be fully discerned. Consider this: An electron microscope can magnify a cell some 200,000 times—an enlargement that would make an ant appear more than half a mile [0.8 km] long. Yet, even at this magnification, some of the cell’s detail is missed!
Scientists have thus found the cell to be amazingly intricate. In his book The Fifth Miracle, physicist Paul Davies states: “Each cell is packed with tiny structures that might have come straight from an engineer’s manual. Minuscule tweezers, scissors, pumps, motors, levers, valves, pipes, chains, and even vehicles abound. But of course the cell is more than just a bag of gadgets. The various components fit together to form a smoothly functioning whole, like an elaborate factory production line.”
DNA—The Molecule of Heredity
Humans as well as multicelled plants and animals start as a single cell. After that cell reaches a certain size, it divides and forms two cells. Then these two cells divide and form four cells. As the cells continue to divide, they specialize—that is, they differentiate, becoming muscle cells, nerve cells, skin cells, and so forth. As the process continues, many of the cells group together to form tissues. Muscle cells, for example, join forces and form muscle tissue. Different types of tissues form organs, such as the heart, the lungs, and the eyes.Underneath the thin covering of each cell lies a jellylike fluid called cytoplasm. Beyond that is the nucleus, which is separated from the cytoplasm by a thin membrane. The nucleus has been called the cell’s control center because it directs nearly all the cell’s activities. Inside the nucleus lies the cell’s genetic program, written in deoxyribonucleic acid—DNA, for short.
DNA molecules lie tightly coiled in the chromosomes of the cell. Your genes, which are sections of the DNA molecules, contain all the information necessary to make you what you are. “The genetic program carried in DNA makes every living thing different from all other living things,” explains The World Book Encyclopedia. “This program makes a dog different from a fish, a zebra different from a rose, and a willow different from a wasp. It makes you different from every other person on the earth.”
The amount of information contained within the DNA of just one of your cells is staggering. It could occupy about a million pages this size! Since DNA is responsible for passing on hereditary information from one generation of cells to the next, it has been called the master plan of all life. But what does DNA look like?
DNA is made up of two strands wound around each other and takes on a shape like that of a spiral staircase or a twisted ladder with rungs. The two strands are connected by combinations of four compounds called bases. Each base of one strand is paired with a base on the other strand. These base pairs form the rungs of the twisting DNA ladder. The exact order of the bases in the DNA molecule is what determines the genetic information it carries. Simply put, this sequence determines virtually everything about you, from the color of your hair to the shape of your nose.
DNA, RNA, and Protein
Proteins are the most abundant macromolecules found in cells. It has been estimated that they account for more than half the dry weight of most organisms! Proteins are made up of smaller building blocks called amino acids. Some of these are made by your body; others must be obtained from your diet.Proteins have many functions. For example, there is hemoglobin, a protein found in red blood cells, which transports oxygen throughout your body. Then there are antibodies, which help your body to ward off disease. Other proteins, such as insulin, help you to metabolize foods as well as regulate various cellular functions. In all, there may be thousands of different kinds of proteins in your body. There may be hundreds within just a single cell!
Each protein carries out a specific function that is determined by its DNA gene. But how is the genetic information in a DNA gene decoded so that a particular protein is made? As shown in the accompanying diagram “How Proteins Are Made,” the genetic information stored in the DNA must first be transferred from the nucleus of the cell into the cytoplasm, where the ribosomes, or protein-producing factories, are located. This transfer is accomplished by means of an intermediary called ribonucleic acid (RNA). The ribosomes in the cytoplasm “read” the RNA instructions and assemble the proper sequence of amino acids to form a particular protein. Thus, there exists an interdependent relationship between DNA, RNA, and the formation of proteins.
Where Did It Begin?
The study of genetics and molecular biology has intrigued scientists for decades. Physicist Paul Davies is skeptical that a Creator could be behind it all. Still, he acknowledges: “Each molecule has a specified function and a designated place in the overall scheme so that the correct objects are manufactured. There is much commuting going on. Molecules have to travel across the cell to meet others at the right place and the right time in order to carry out their jobs properly. This all happens without a boss to order the molecules around and steer them to their appropriate locations. No overseer supervises their activities. Molecules simply do what molecules have to do: bang around blindly, knock into each other, rebound, embrace. . . . Somehow, collectively, these unthinking atoms get it together and perform the dance of life with exquisite precision.”With good reason, many who have studied the inner workings of the cell have concluded that there must be an intelligent force responsible for its creation. Let us consider why.
What Is Behind the Mystery of Life?
THE DNA molecule does amazing things. DNA fulfills both the roles that your cells require of genetic material. First, the DNA is accurately duplicated so that information can be passed on from cell to cell. Second, the DNA sequence tells the cell what proteins to make, thereby determining what the cell will become and what function it will serve. However, DNA does not carry out these processes on its own. Many specialized proteins are involved.DNA alone cannot create life. It contains all the instructions needed to make all the proteins a living cell needs, including the very ones that copy DNA for the next cell generation and the ones that help DNA to make new proteins. Still, the incredible amount of information stored in the DNA genes is useless without RNA and the specialized proteins, which include ribosomes, needed to “read” and use that information.
Neither can proteins alone produce life. An isolated protein cannot generate the gene that has the code for making more of that same type of protein.
So, what has unraveling the mystery of life shown? Modern genetics and molecular biology have provided ample evidence of the highly complex and interdependent relationships between DNA, RNA, and protein. These findings imply that life depends on having all these elements simultaneously. Thus, life could never have come about spontaneously by chance.
The only reasonable explanation is that a supremely intelligent Creator coded the instructions in DNA and simultaneously made the fully formed proteins. The interaction between them was so well devised that once begun, this process would ensure that proteins would continue to copy DNA to make more genes, while other proteins would decode genes to make more proteins.
Clearly, the marvelous cycle of life was set in motion by the Master Designer, Jehovah God.
Wonderfully Made
Although it is not a scientific book, the Bible sheds some light on the role of the Creator, who designed the code of life. Some three thousand years ago, King David of Israel, who knew nothing of today’s advances in genetic research, said in poetic language to his Creator: “It was you who created my inmost self, and put me together in my mother’s womb; for all these mysteries I thank you: for the wonder of myself, for the wonder of your works. You know me through and through, from having watched my bones take shape when I was being formed in secret, knitted together in the limbo of the womb.”—Psalm 139:13-15, Jerusalem Bible.So take another 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 basic shape of your body. Think of how these characteristics were inherited from generations past and how they are transferred to your offspring. Now, give some thought to the One who put in order this marvelous mechanism. You may be moved to repeat the words written by the apostle John: “You are worthy, Jehovah, even our God, to receive the glory and the honor and the power, because you created all things, and because of your will they existed and were created.”—Revelation 4:11.