Thread of Life Pt 1

The Bell Telephone System brings you another of its series of programs on science. Man's effort to understand nature's laws. The story you are going to see and hear is about science. It is also a story about you. This man is a geneticist. He is concerned with questions that have puzzled mankind for many ages. How is the spark of life passed on from father and mother to daughter and son? How does heredity work? Exploring the tiny universe under the microscope, he studies the wonderful way in which life is passed on from one living cell to the next. For in these little units of which all living things are made, lies hidden the secret which we may well call the thread of life. [Music] We are about to unfold for you an adventure in the world of science. A science that deals with the nature of living things. Our story is about you and me and why we are alike in some ways and yet why each person is different from every other. There are billions of people over the face of the earth of all sizes, shapes, dispositions. Let's look at a few examples. Nature arranges endless combinations. [Music] How does nature endow us with many different traits or characteristics. Well, that's what our show is about. Through the magic of electronics, we're inviting some of the audience to come along with us and join in. Dr. Baxter. Oh, yes. Hello. Can I ask a question? Surely. You see, I'm left-handed. Yes, sir. And my dad is left-handed, too. So, I must have inherited that from him, huh? Very likely. Uh, does your dad have blue eyes, too? Well, sure. But, well, maybe you're a chip off the old block, then, because being left-handed and having blue eyes are both traits you could have inherited, Dr. Baxter. Oh, yes. Hello. You'll notice I have a white forlock and very fashionable, but I've heard a lot of odd stories about what causes such things. Yes, but most of them are only old wives tales. The truth is, it's just another inherited trait. like this gentleman's high forward and heavy brows. Well, here's what's been puzzling us. Our baby has red hair. And both of us have brown hair. No mystery. Parents can hand down a trait that's hidden in themselves. In fact, a trait like red hair can be hidden for many generations. The story of how heredity is passed on from generation to generation is the same for all living things, human beings, animals, plants, even the lowliest creatures. Let's go to the microscope and look at one of nature's simpler animals, an amoeba, an organism that has only one cell. And like every living thing, this little cell is a sort of chemical machine carrying on the many intricate functions we call life. One of the functions is to reproduce. Watch. We can see it [Music] divide. Now there are two daughter cells. The two new cells are just like the old one. They inherited all the traits of the cell they came from. And this same sort of process goes on in all living creatures. I see. Now you've got two cells. Okay. But what I'd like to know is where'd the first cell come from? In a way, you're asking where life itself began. We don't know that. But the first cell you saw here came from some other cell. All cells come from other cells. That's how the chain of life has come down through the ages. You started life as a single cell. That cell was a combination of an egg like this from your mother and a sperm cell from your [Music] father. You are seeing actual motion pictures of a human egg in the process of fertilization. Many sperm are trying to enter the egg. Only one can fertilize it. When egg and sperm cells like these joined, you came into existence. When the fertilized egg is only hours old, it begins to divide. It divides over and over [Music] again. The new cells begin to work in different ways. Some become muscles, others make nerves. Here bone making cells, skin cells, blood cells, trillions of cells, an embryo takes shape. Then the greatest miracle of all, a baby. And not just any baby, but a baby of a particular kind. A baby with almond shaped eyes or round eyes, with brown skin or white skin? All this begins with one tiny egg, no bigger than the tiniest dot that you can make with a sharp pencil. But can you predict what an egg is going to grow into? Can you tell by looking at it? No, you can't. Many egg cells look very much alike. Look at this egg or this one or this one. Could you guess that one would become a baby, one a rabbit, one a lamb? And when we analyze the cells of various living things and find that their chemical machinery is about the same, we begin to wonder what shapes the development of a living being. All right. A lot of cells look the same. Their chemical machinery, as you call it, is about the same. But still, there must be some sort of a gimmick inside the cell that makes it work. You're right. And scientists have been trying for a long time to find that gimmick. But the first clue to the workings of heredity was uncovered in a way that might surprise you. How is that? By mathematics. In one of the greatest achievements of the human mind. The story begins over a hundred years ago in a monastery in a corner of the old Austrian Empire. There lived a monk named Gregor Mendel, a teacher, a man of many talents. Driven by his scientific curiosity, he spent long, busy hours working over a patch of peas in the monastery garden. He noted that some of the traits of the pea plants were clear and distinct. Some of the strains were always tall, some were always short, some had wrinkled peas, some smooth peas, some purple flowers, some white. And he set out to determine how these traits were passed on from one generation to the next. He cross-pollinated large numbers of the plants, and he kept careful records. After eight years of painstaking work, he reported his findings to the scientific society in the town of Brun. And so, gentlemen, I crossed a pure strain of tall plants with pure short plants by putting some pollen from one strain onto the flower of the other. You might suppose that their offspring would be medium-siz plants, but not. So, the next generation were all tall plants. And now when I cross these plants among themselves, 3/4s of the grandchildren came out tall and 1/4 came out short. On an average, tall plants outnumber the short by just about 3 to one. How does this happen? From tall and short parents, all tall children. And from tall children, a mixture of grandchildren that are both short and tall. This is my theory. Our original parents were pure strains. So each child inherited a unit for tallness, then a unit for shortness, but they all grew tall. That's because tallness is a strong or dominating trait. I call it dominant. While shortness is weaker, or as I call it, recessive. Now these child plants are not pure strains even though they are tall because each contains a unit for shortness which is hidden or blocked by the dominant unit for tallness but it is still there waiting. So when these child plants are crossed with each other a grandchild plant has four equal chances. It may get a tall unit from each parent and be a pure tall plant like the tall grandparent. a short unit from each parent becoming a short plant like the short grandparent or a tall and a short and become tall or a short and a tall and become tall and thus an average of three plants will be tall for each one that is short. Tallness and shortness are due to hereditary units. Using thousands of plants, I have studied six other traits for color of blossoms, shape of pods, color and texture of peas and so on. And these traits too are inherited as units. Units that are passed on from generation to generation. And in every generation, they are shuffled and reshuffled according to the laws of chance. That I believe is what causes the puzzling mixture of traits in nature. Gregor Mendel died January 6th, 1884. His work was unnoticed by the world, but his careful study of nature had begun to explain one of her great mysteries. He proved the existence of something that could not be seen. The invisible units of heredity. The same units that govern your hair color or the shape of your face or make your eyes blue. But what were these units? How did they work? These were problems other scientists had to work [Music] out. It was in 1866 that Gregor Mendel's report to the scientific society was published. But years passed before the scientific world was ready to see its value. Now these units, the ones that Mendele discovered, units of heredity, he he proved they were there. But where? I thought we'd already found out. In the cell. That's right. Well, could they be some kind of particles? Exactly my question. That's also the question biologists began to ask themselves. And for the answer, they looked deep into the unit of life with their microscopes inside the cell and probed into its inner core, the nucleus. Can you see inside a nucleus with a microscope? Yes, it's not easy because ordinarily all you see of the nucleus is a fuzzy indistinct blob. But when scientists stain the cells with a strong dye, some parts begin to show up and we see strange little fibers called chromosomes. There are chromosomes in the cells of every living organism. They come in matched pairs. In every cell of corn, for example, there are 10 pairs or 20 chromosomes. The grasshopper, 24 chromosomes, and man, 46, 23 pairs. Well, man has the most. Is that because man is the highest form of life? No, because a potato has 48 chromosomes. Some goldfish have 94. One kind of crayfish has about 200. The number doesn't seem to be significant. But what the chromosomes do is very significant. Suppose we look through a microscope at chromosomes in a live cell. You're about to see some extraordinary motion picture scenes. They were photographed by Dr. An buyer, Mrs. Byer, and Crackco Poland by coupling a motion picture camera with a microscope. Here you see several cells dividing and forming new cells in the act of growth, a process called mitosis. The cycle we are watching takes about half a day in nature, but we are seeing it in speed up timelapse photography. Now, let's look at a single cell as it divides. Watch the chromosomes closely. Each one will split into two identical new chromosomes. The new chromosomes now separate into two clusters, each becoming part of a newly formed nucleus. A dividing wall will form and we will have two new cells. Each new cell has the same chromosomes as the old cell. Well, that's very clear. Well, sure. And they pass them on from one cell to the next, you might say. And does that mean that heredity is carried by the chromosomes? But you said those units were invisible. We can see chromosomes. Right. And what you are all asking are precisely some of the questions that occurred to scientists around the turn of the century. About this time, Mendle's forgotten report was discovered and brought to the attention of the world. Meanwhile, scientists looking in microscopes found that chromosomes followed the same rules of behavior as mendle's units. And the same idea occurred to several investigators at almost the same time. The units of heredity are carried on the chromosomes. This idea led the way to the birth of a whole new branch of science, genetics. All based on the invisible particles now called genes which are passed on from generation to generation. First discovered by a patient dedicated scientist working alone in a monastery garden. Man without even a microscope. That's another reminder that the most powerful instrument in the cause of science is the human mind. All right, let's back up a minute. Genes are on chromosomes. Yes, but you can't see them. The fact is scientists are still not quite sure what to look for, but they're getting closer. They're beginning to find more and more of how the genes work. If scientists couldn't see the genes, how could they be so sure they were on the chromosomes? Well, let's ask this scientist. We have several ways of knowing, Dr. Baxter. One way is by means of experiments on Dresophila, a harmless little insect commonly known as the fruitfly. Human chromosomes are too small and too numerous to be examined in detail. But the chromosomes found of all places in the salivary gland of a fruitly are huge, as if tailor made for scientific study. By experiment, we can prove that the units or the genes are actually lined up in single file along the chromosomes. And we're able to locate the exact position of hundreds of genes. Now, this black band, for example, is the location of a gene that's responsible for eye pigment. How do we know this for sure? Because in fruit flies where this segment is missing, the eyes have no pigment and appear white. Down here we know is a gene necessary for normal wings. Here for body color and so on. On this particular chromosome, we know the location of more than a 100 genes. The lineup of genes on the chromosomes of the fruitfly is as clear to the geneticist as towns on a railroad line. In fact, he calls his diagrams of them chromosome maps. Maps like these were constructed on a theoretical basis as long ago as 1916 by the brilliant insight of the geneticist Thomas Hunt Morgan and his students. We don't have a map of the human chromosomes yet, but we know the genes are there. We know that they determine what our cells will do and what we will be like. And do I have the same genes in every cell? In practically every cell in your body, but what's the use of having a blue-eyed gene in my big toe? Nobody knows. And wouldn't scientists like to think up an experiment that would answer that question? Well, then where do I get my genes in the first place? From your father and mother, of course. The idea is this. Your heredity comes to you in two bundles. The sperm cell from your father with its 23 chromosomes and the egg from your mother with another 23. But I thought you just told us that a human cell has 46 chromosomes. That's right. With the one exception of egg and sperm cells. You see, nature's arithmetic has to come out right. So you get 23 chromosomes from your mother and 23 from your father. Each parent contributes only half. And in this way you get the normal number of 46 chromosomes in the fertilized egg from which you grow. Does that mean I have just part of my father's genes? That's right. Only half and half of your mother's. Well, what decides which ones I get? The rule for human beings is just the same as menal found with peas. Chance, pure chance. You see, the egg and the sperm are formed in a different way from all the other cells of your body. And the way they are made is one of the most beautiful and ingenious of all nature's processes. They are formed by special germ cells, each with a normal number of 46 chromosomes. Let's look at just one half of the picture, the father's side. This cell is going to divide in order to form sperm cells. It has the normal number of 46 chromosomes. 23 from the man's mother, 23 from his father. But it doesn't divide the way other cells do. This cell follows a different process called meiosis. First, the chromosomes match up in pairs. The pairs move around in the cell. Then each chromosome splits in two, each side carrying only one half the genes. And as though a signal, all the chromosomes draw apart into two equal groups on either side of the cell. Then the whole cell divides and subdivides into four sperm cells each carrying with it 23 chromosomes and 1/2 of the original genes. Which combination of chromosomes goes into which sperm cell is a matter of chance. A similar process goes on in the forming of the egg cell. And the coming together of these two chance combinations starts that unique and wonderful creation we call a human being. Then you really can't predict how things will come out. No more than you can foretell the toss of a coin. Both are governed by that complexity of unknown causes which we call chance. And just as a little demonstration, let me show you the mathematical chances involved in your heredity. Some of you may not realize the number of combinations that are possible with 46 chips. Now, here are 23 representing mother's chromosomes, 23 for fathers, and each chip has two sides, of course, because the chromosomes of both parents come in pairs. Now, we put them together. [Applause] and throw them out. Do you know what the chances are that this very same combination of 46 sides will turn up again? Well, the odds against it are 70 million million to one. That means the chances of your being exactly like your brother or sister are less than 1 in 70 million million. This is many times the total number of people who ever lived. So the chances of two persons happening to be just alike are slim indeed. But I know two sisters who are as alike as two peas in a pod. Oh, of course. Even if brothers and sisters heredities are not exactly alike, they're bound to have many identical genes. The more they happen to share, the more clearly we see a family resemblance. And in certain cases, children have exactly the same heredity. Gene for gene. These are identical twins. Identical twins begin life as one fertilized egg. This egg divides at first in the normal way. But early in its growth, the embryo splits into two. And of course, in every cell of both embryos are the same chromosomes and the same genes. That's why such twins are always the same sex and so astonishingly alike. Getting back to the average case though, a lot of genes come shuffling down through my family until they come together and bingo, that's me. But I don't see how they do it. How can some little gizmos in the chromosomes stuck away in the nucleus of a cell? How can they curl your hair or make your ears stick out? It's only in recent years that we've begun to find out how genes do their work. And as research and experiments go on, scientists are opening a new and fascinating chapter in the science of the genes, genetics. [Music]