{QTtext}{timescale:100}{font:Arial}{size:18}{backColor:0,0,0} {textColor:65535,65535,65535}{width:340}{justify:left} [00:00:00.00] [00:00:00.45] The Bell Telephone System brings you another of its series of programs on science. [00:00:05.95] Man's effort to understand nature's laws. [00:00:12.03] The story you are going to see and hear is about science. [00:00:15.77] It is also a story about you. [00:00:18.58] This man is a geneticist. He is concerned with questions that have puzzled mankind for many ages. [00:00:26.02] How is the spark of life passed on from father and mother to daughter and son. How does heredity work? [00:00:35.66] 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. [00:00:44.33] 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) [00:01:28.38] We are about to unfold for you an adverture in the world of science, the science that deals with the nature of living things. [00:01:36.28] 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. [00:01:45.66] There are billions of people over the face of the earth, all sizes, shapes, dispositions. Let's look at a few examples. [00:01:55.06] Nature arranges endless combinations. [00:02:29.20] How does nature endow us with so many different traits or characteristics? Well, that's what our show is about. [00:02:36.08] Through the magic of electronics, we're inviting some of the audience to come along with us and join in. [00:02:42.61] Dr. Baxter. [00:02:43.95] Oh, yes, hello. [00:02:45.42] Can I ask a question? [00:02:46.95] Surely. [00:02:48.28] You see, I'm left-handed. [00:02:50.22] Yes, sir. [00:02:51.86] And my Dad's left-handed too. So, I must have inherited that from him, huh? [00:02:57.69] Very likely, but does your Dad have blue eyes too? [00:03:01.27] well sure, but [00:03:02.83] 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. [00:03:11.77] Dr. Baxter. [00:03:13.20] Oh, yes, hello. [00:03:14.73] You noticed I have a white forelock. [00:03:16.91] And very fashionable. [00:03:18.41] But I've heard a lot of odd stories about what causes such things. [00:03:22.02] Yes, but most of them are only old wives tales. The truth is, it's just another inherited trait [00:03:29.48] like this gentleman's high forehead and heavy brows. [00:03:32.92] Well here's what's been puzzling us. Our baby has red hair. [00:03:37.59] And both of us have brown hair. [00:03:40.06] 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. [00:03:50.20] 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. [00:04:02.39] Let's go to the microscope and look at one of nature's simpler animals, an amoeba, an organism that has only one cell. [00:04:11.17] And like every living thing, this little cell is a sort of chemical machine, carrying on the many intricate functions we call life. [00:04:20.55] One of the functions is to reproduce. Watch. [00:04:25.25] We can see it divide. [00:04:33.69] Now there are two daughter cells. The 2 new cells are just like the old ones. [00:04:39.86] They inherited all the traits of the cell they came from. And this same sort of process goes on in all living creatures. [00:04:49.20] I see. Now you've got 2 cells. Ok. But what I'd like to know is, where'd the first cell come from? [00:04:57.34] In a way, you're asking where life itself began. We don't know that. [00:05:02.75] 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. [00:05:14.39] 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 father. [00:05:30.91] You're 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. [00:05:43.33] When egg and sperm cells like these join, you came into existence. When the fertilized egg is only hours old, it begins to divide. It divides over and over again. [00:06:06.02] The new cells begin to work in different ways. Some become muscles. [00:06:11.69] Others make nerves. [00:06:14.69] Here, bone making cells, [00:06:17.78] skin cells, [00:06:20.36] blood cells, [00:06:22.80] trillions of cells. An embryo takes shape. Then, the greatest miracle of all - [00:06:31.03] a baby. And not just any baby, but a baby of a particular kind. [00:06:37.00] a baby with almond shaped eyes [00:06:39.84] or round eyes [00:06:41.94] with brown skin [00:06:43.92] or white skin [00:06:46.25] All this begins with one tiny egg, no bigger than the tiniest dot that you could make with a sharp pencil. [00:06:54.36] But can you predict what an egg is going to grow into? Can you tell by looking at it? [00:07:00.06] No, you can't. [00:07:02.91] Many egg cells look very much alike. [00:07:06.38] Look at this egg. [00:07:09.27] or this one [00:07:12.11] or this one [00:07:14.88] could you guess that one would become a baby [00:07:22.08] one a rabbit [00:07:24.92] one a lamb [00:07:27.98] 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? [00:07:41.47] 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. [00:07:54.19] You're right. Scientists have been trying for a long time to find that gimmick, [00:07:59.86] but the first clue to the workings of heredity was uncovered in a way that might surprise you. [00:08:05.53] How was that? [00:08:07.03] By mathematics. [00:08:11.44] In one of the greatest achievements of the human mind. [00:08:15.58] The story begins over 100 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 scientific curiosity. [00:08:31.69] He spent long busy hours working over a patch of peas in the monastery garden. [00:08:36.53] He noticed that some of the traits of the pea plants were clear and distinct. Some of the strains were always tall. [00:08:45.86] Some were always short. [00:08:48.38] Some had wrinkled peas, [00:08:50.06] some smooth peas. [00:08:52.17] Some had purple flowers, [00:08:54.14] some white. [00:08:56.08] And he set out to determine how these traits were passed on from one generation to the next. [00:09:03.42] He cross pollinated large numbers of the plants and he kept careful records. [00:09:09.39] After 8 years of painstaking work, he reported his findings to the scientific society in the town of Brunn. [00:09:17.56] 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. [00:09:28.41] You might suppose that their offspring would be medium size plants, but not so. [00:09:34.02] The next generation were all tall plants. [00:09:37.61] And now when I cross these plants among themselves, 3/4 of the grandchildren came out tall, and 1/4 came out short. [00:09:45.80] On an average tall plants outnumber the short by just about 3 to 1. How does this happen? [00:09:54.73] 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 - [00:10:06.28] Our original parents were pure strains. So each child inherited a unit for tallness and a unit for shortness, but they all grew tall. [00:10:16.69] That's because tallness is a strong or dominating trait. I call it dominant; while shortness is weaker, or as I call it, recessive. [00:10:27.94] 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, [00:10:42.28] so when these child plants are crossed with each other, a grandchild plant has 4 equal chances. [00:10:49.28] It may get a tall unit from each parent and be a pure tall plant like the tall grandparent, [00:10:55.19] a short unit from each parent becoming a short plant like the short grandparent, [00:10:59.73] or a tall and a short and become tall, [00:11:03.20] or a short and a tall and become tall. [00:11:07.20] And thus, an average of 3 plants will be tall for each one that is short. [00:11:12.81] Tallness and shortness are due to hereditary units. [00:11:19.05] Using thousands of plants I have studied 6 other traits for color of blossoms, shape of pods, color and texture of peas, and so on. [00:11:28.69] And these traits too are inherited as units. Units that are passed on from generation to generation. [00:11:36.86] And at every generation they are shuffled and reshuffled according to the laws of chance. [00:11:43.70] That I believe is what causes the puzzling mixture of traits in nature. [00:11:53.98] Gregor Mendel died January 6, 1884. [00:12:00.83] His work was unnoticed by the world, but his careful study of nature had begun to explain one of our great mysteries. He proved the existence of something that could not be seen, the invisible units of heredity. [00:12:18.38] The same units that govern your hair color or the shape of your face or make your eyes blue. [00:12:25.75] But what were these units? How did they work? These were problems other scientists had to work out. [00:12:35.36] 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. [00:12:50.44] Now these units, the ones that Mendel discovered, [00:12:54.14] units of heredity [00:12:55.51] He proved they were there but where? [00:12:58.42] I thought we already found out - in the cell. [00:13:01.59] That's right. [00:13:03.33] Well, could they be some kind of particle? [00:13:06.00] Exactly my question. [00:13:09.06] That's also the question biologists began to ask themselves. [00:13:14.20] 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. [00:13:23.65] Can you see inside a nucleus with a microscope? [00:13:27.39] Yes. It's not easy, because ordinarily all you see of the nucleus is a fuzzy, indestinct blob. [00:13:35.05] But when scientists stain the cell with a strong die, some parts begin to show up and we see strange little fibers called chromosomes. [00:13:46.00] There are chromosomes in the cells of every living organism. They come in matched pairs. [00:13:53.11] In every cell of corn, for example, there are 10 pairs or 20 chromosomes. [00:13:58.94] The grasshopper, 24 chromosomes. [00:14:04.06] and man, 46 (23 pairs). [00:14:08.56] Well, man has the most. Is that because man is the highest form of life? [00:14:15.03] No, because a potato has 48 chromosomes. [00:14:21.34] Some goldfish have 94. [00:14:24.22] One kind of crayfish has about 200. [00:14:27.92] The number doesn't seem to be significant. What the chromosomes do is very significant. Suppose we look through a microscope at chromosomes in a live cell. [00:14:39.39] You are about to see some extraordinary motion picture scenes. They were photographed by Dr. Anje Byer and Mrs. Byer in Krakow, Poland, by coupling a motion picture camera with a microscope. [00:14:51.61] Here you see several cells dividing and forming new cells in the act of growth, a process called mitosis. [00:14:59.92] The cycle we are watching takes about half a day in nature, but we are seeing it in speed-up, time-lapse photography. [00:15:08.42] Now let's look at a single cell as it divides. Watch the chromosomes closely. Each one will split into 2 identical new chromosomes. [00:15:21.03] The new chromosomes now separate into 2 clusters, each becoming part of a newly formed nucleus. [00:15:30.48] A dividing wall will form, and we will have 2 new cells. [00:15:36.65] Each new cell has the same chromosomes as the old cell. Well that's very clear. [00:15:41.59] Well, sure, and they pass them on from one cell to the next, you might say. [00:15:47.00] And does that mean that heredity is carried by the chromosomes? [00:15:51.17] But you said those units were invisible. We can see chromosomes. [00:15:55.53] Right. And what you are all asking are precisely some of the questions that occured to scientists around the turn of the century. [00:16:03.44] About this time Mendel's forgotten report was discovered and brought to the attention of the world. [00:16:10.08] Meanwhile, scientists looking in microscopes found that chromosomes followed the same rules of behavior as Mendel's units. And the same idea occurred to several investigators at almost the same time. [00:16:23.59] The units of heredity are carried on the chromosomes. [00:16:28.36] This idea led the way to the birth of a whole new branch of science, [00:16:32.53] 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. [00:16:48.50] Man, without even a microscope. [00:16:52.77] That's another reminder that the most powerful instrument in the cause of science is the human mind. [00:16:59.05] All right, let's back up a minute. Genes are on chromosomes. [00:17:05.39] Yes. [00:17:06.47] but you can't see them [00:17:08.53] 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. [00:17:17.11] If scientists couldn't see the genes, how could they be so sure they were on the chromosomes? [00:17:21.75] Well, let's ask this scientist. [00:17:26.69] We have several ways of knowing, Dr. Baxter. One way is by means of experiments on Drysophilla, a harmless little insect commonly known as the fruit fly. [00:17:37.73] 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 fruit fly are huge, as if taylor made for scientific study. [00:17:53.98] 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 100's of genes. [00:18:09.28] 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? [00:18:19.12] because in fruit flies where this segment is missing, the eyes have no pigment and appear white. [00:18:25.11] Down here we know there's a gene necessary for normal wings, [00:18:31.12] here for body color, and so on. On this particular chromosome we know the location of more than 100 genes. [00:18:40.56] The line up of genes on the chromosomes of the fruit fly is as clear to the geneticist as towns on a railroad line. In fact he calls his diagrams of them chromosome maps. [00:18:58.38] 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. [00:19:11.65] 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. [00:19:21.47] And do I have the same genes in every cell? [00:19:24.44] In practically every cell in your body. [00:19:26.94] Well what's the use of having a blue-eyed gene in my big toe? [00:19:30.48] Nobody knows. And wouldn't scientists like to think up an experiment that would answer that question. [00:19:36.51] Well, then, where do I get my genes in the first place? [00:19:40.51] from your father and mother, of course [00:19:42.92] The idea is this. Your heredity comes to you in 2 bundles, [00:19:50.03] the sperm cell from your father, with its 23 chromosomes, [00:19:55.90] and the egg from your mother with another 23. [00:20:00.47] But I thought you just told us that a human cell has 46 chromosomes. [00:20:04.88] That's right, with the one exception of egg and sperm cells. [00:20:09.20] You see, nature's arithmetic has to come out right. So you get 23 chromosomes from your mother and 23 from your father. [00:20:19.00] 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. [00:20:29.90] Does that mean I have just part of my father's genes? [00:20:32.73] That's right, only half, and half of your mother's. [00:20:36.64] Well, what decides which ones I get? [00:20:39.34] The rule for human beings is just the same as Mendel found with peas: chance, pure chance. [00:20:46.01] 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. [00:20:59.17] They are formed by special germ cells, each with the normal number of 46 chromosomes. Let's look at just 1/2 of the picture, the father's side. [00:21:08.84] 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, and 23 from his father, [00:21:21.86] but it doesn't divide the way other cells do. This cell follows a different process called meiosis. [00:21:29.83] First the chromosomes match up in pairs. The pairs move around in the cell. [00:21:38.06] Then each chromosome splits in two, each side carrying only 1/2 the genes, and as though at a signal, all the chromosomes draw apart into 2 equal groups on either side of the cell. [00:21:55.09] Then the whole cell divides and sub-divides into 4 sperm cells, each carrying with it 23 chromosomes and 1/2 of the original genes. [00:22:06.65] Which combination of chromosomes goes into which sperm cell is a matter of chance. [00:22:12.53] A similar process goes on in the forming of the egg cell. [00:22:17.88] And the coming together of these 2 chance combinations starts that unique and wonderful creation we call a human being. [00:22:26.45] Then you really can't predict how things will come out? [00:22:29.75] No more than you can foretell the toss of a coin. Both are governed by that complexity of unknown causes which we call chance. [00:22:38.09] 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. [00:22:50.88] Now here are 23 representing mother's chromosomes, [00:22:55.01] 23 for father's. [00:22:57.64] And each chip has 2 sides, of course, because the chromosomes of both parents come in pairs. [00:23:05.19] Now, we put them together. [00:23:30.14] And throw them out. [00:23:36.58] 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. [00:23:49.47] That means the chances of your being exactly like your brother or sister are less than 1 in 70 million million. [00:23:58.56] This is many times the total number of people who ever lived. So the chances of 2 persons happening to be just alike are slim indeed. [00:24:06.25] Well, I know 2 sisters who are as alike as 2 peas in a pod. [00:24:12.51] Oh, of course. Even if brother's and sister's heredities are not exactly alike, they're bound to have many identical genes. [00:24:20.75] 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. [00:24:31.11] These are identical twins. Identical twins begin life as one fertilized egg. [00:24:36.98] 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. [00:24:50.83] That's why such twins are always the same sex and so astonishingly alike. [00:24:58.59] 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. [00:25:10.34] How can some little gizmos in the chromosomes stuck away in the nucleus of the cell, how can they curl your hair? [00:25:18.72] or make your ears stick out? [00:25:20.81] It's only in recent years that we've begun to find out how genes do their work. [00:25:24.63] And as research and experiments go on, scientists are opening a new and fascinating chapter in the science of the genes, genetics. [00:25:49.59] (music) [00:25:57.14] We know that the genes seem to be the blueprint for each cell, designing and determining what it does. [00:26:05.03] We also know that each living cell is like a tiny chemical machine. Genes control the chemical reactions, and in this way they affect all our body functions. [00:26:16.31] These functions often differ from one creature to another, even from one person to the next according to the genes. [00:26:23.95] For example, you might think that everything tastes the same to everybody. That's not always true. It depends on heredity. [00:26:35.06] Take this family group. We'll make a simple chemical test anybody can do. These papers contain a harmless chemical we call PTC. I want each of you to put a strip in his mouth. [00:26:48.62] Now some of you will be able to taste it, and others won't. And if you can taste it, it's going to taste bitter. Don't worry. It's harmless. The ability to taste PTC is a dominant inherited trait just like tallness in Mendel's pea plants. [00:27:06.93] Let's consider the case of this baby who can't drink milk. [00:27:11.34] Most babies, of course, thrive on a milk diet, [00:27:15.34] but this one has a peculiarity in his body chemistry. His body can't handle one of the sugars found in milk, a sugar called galactose. [00:27:24.56] Medical records showed that the baby's ailment is inherited. It's a matter of genes, genes that control the way sugar is used in the body. [00:27:34.53] Go ahead. [00:27:36.59] Well, [00:27:38.03] Question? [00:27:39.19] Yes, well that is - Is it genes that tell whether a baby will be a boy or a girl? [00:27:46.26] Yes they do. A little while ago you remember, we found that the genes are on the chromosomes. We also got the idea that all of our 46 chromosomes are in 23 matched pairs. [00:28:03.05] Actually there's a very important exception. In every male human being the 23rd pair of chromosomes is a mismatch, one large partner and one short one. [00:28:17.33] We call them an X chromosome and a Y. [00:28:21.39] In the cells of every female human being there are 2 X chromosomes and no Y. [00:28:28.06] A fertilized egg that has 2 X's will grow into a girl. [00:28:32.40] One that has an X and a Y can only grow into a boy. Which parent determines which types the fertilized egg will have? [00:28:41.19] It can't be the mother, because she has no choice. She can only contribute an X chromosome, [00:28:48.06] but father in his cells has one of each, an X and a Y. And the sperm that fertilizes the egg can carry either an X or a Y. The chances are 50/50. [00:29:00.97] If the father's sperm cell contains an X, the baby will be a girl. [00:29:06.40] If a Y, a boy will be born. Father's chromosomes decide. [00:29:12.14] I suppose that's why fathers brag so much. [00:29:16.33] Well, fathers may brag, but on the other hand, the Y seems to carry nothing much except the genes that determine male sex. [00:29:26.01] While the X chromosome carries a variety of genes. This arrangement leads to interesting consequences. [00:29:33.98] For instance women are a lot less apt to be colorblind than men. [00:29:39.34] Yes, I've heard that's true, and I've always wondered why. [00:29:42.50] Well, the gene for colorblindness is a recessive that's carried on an X chromosome. If a girl inherits this gene, she usually has a dominant normal gene on her other X chromosome to suppress it. [00:29:58.15] So this girl would have normal color vision. [00:30:01.97] While if a boy inherits the same gene, there is no dominant gene for normal color vision on the little Y to suppress it, so he'll be colorblind. [00:30:16.34] If you think about it, you'll recall that nearly all the colorblind people you've known have been men or boys. Now you know the reason. And for this reason, colorblindness is called a sex linked trait. [00:30:29.83] Say, wouldn't baldness be a sex linked trait? [00:30:32.89] You might think so, but it's not. The baldness gene is on a different pair of chromosomes. But for some reason it produces its affect only in the presence of the male sex hormone. [00:30:45.20] When a woman carries the gene for baldness, nothing happens. When a man carries the gene, then you get this eminently resplendent effect. [00:30:57.45] Dr. Baxter. [00:30:59.39] Hello, this is your first appearance, I believe. Question, young lady? [00:31:04.42] Yes, sir. Everything you've shown us and talked about is heredity. Isn't environment really more important? [00:31:12.33] Of course, environment is enormously important. Every gardener knows that plants grow better when they are watered and tended. [00:31:19.90] Mendel's tall peas grew even taller when he planted them in good soil, [00:31:25.38] and your good health and your good looks are partly due to good genes, but they're also due to good food and happy surroundings. You're a product of both your heredity and your environment. [00:31:40.45] Well, then let me ask you this question. Can you inherit the effects of a good or a bad environment? [00:31:46.36] That question has been studied and discussed for a long time, and the answer is no. We can have our blood replaced by a transfusion of somebody else's blood, [00:31:57.94] or develop spectacular muscles by weight lifting, [00:32:02.51] but none of these changes can be passed on to our children. [00:32:06.62] Well yes, but heredity has to change. [00:32:08.72] Has to? [00:32:09.69] Well, I mean, well not in one generation, but over the long haul a lot of genes must have changed. Otherwise people today would look like they did in the days of the caveman. [00:32:21.20] Yes, genes do sometimes change. Heredity changes. The changes are called mutations. Such changes down through the ages is the basis of evolution. [00:32:33.08] The camel that you see now a days once looked like this. Every now and then on rare occasions, nature strikes a wrong key. [00:32:44.39] Well now, back up please. Nature strikes a wrong key? [00:32:49.83] Every now and then, about once in a 100,000 generations or more, a gene doesn't copy itself exactly, pulls a boner. [00:32:59.59] And this is called a mutation? [00:33:01.56] Yes, and if this mistake occurs in a germ cell, it can be inherited. [00:33:07.83] These mice are victims of gene mutations, one dwarf, one too fat, [00:33:15.84] one born hairless and one with skin like a rhinocerous. [00:33:21.98] This pour creature, because of a mutation affecting his nervous system, is condemned to spend his whole life running in circles. [00:33:31.26] Mutations like these are harmful, of course, but sometimes mutations show up in pleasant or beneficial changes. These stunning goldfish are descendants of mutated fish. [00:33:43.90] So were the mink that produced this beautiful pastel coat. [00:33:49.54] We don't know yet precisely how a gene changes, but we have some pretty good ideas. And once a gene does change, it can be passed on only in its new form. It becomes a regular part of heredity from that time on. [00:34:05.02] Plant breeders have taken a lot of practical advantage of nature's mutations. By discovering new strains and breeding them, it's been possible to grow more and better food in many countries. [00:34:16.63] Farmers often lose crops of wheat because of wheat rust. Breeders have discovered some strains that are resistant to rust and perpetuated them. [00:34:28.34] This crop is immune. [00:34:33.42] All over the world hybrid corn genetically bred has saved farmers and consumers millions of dollars and greatly increased our supply of food. [00:34:52.05] The principles of genetics have also been put to work in breeding poultry for market and for egg production, [00:35:00.51] in breeding hogs and beef cattle, [00:35:05.62] in growing oranges and grapefruit, [00:35:09.33] lumber trees in Sweden, [00:35:11.73] and rice in Japan. [00:35:14.25] Witness this most fabulous genetic creation, a seedless watermelon, developed by Dr. Hitoshi Kihara and his associates in Japan. [00:35:24.97] Oh, it looks mighty good. [00:35:26.80] Dr. Baxter, I can see how scientists do wonderful things with nature's mutations, but I was wondering, do they know how to cause mutations? [00:35:36.83] Yes, they do. Man-made mutations are one of the important scientific questions for the modern world. [00:35:47.86] Scientists have found that mutations can be artificially induced in several ways. [00:35:55.84] Back in 1926 working in his lab at the University of Texas, Dr. Hermann J. Muller began some new experiments. [00:36:07.12] He set up an x-ray machine in his laboratory. His purpose was to see if mutations could be caused by radiation. [00:36:15.16] He conducted his x-ray experiments on the fruit fly. X-rays can produce some striking abnormalities among the descendants of irradiated fruit flies: [00:36:26.47] nearly wingless flies, [00:36:28.97] flies with extra wings, [00:36:32.44] flies with curly wings, [00:36:35.91] flies with black bodies, [00:36:39.05] white-eyed flies. [00:36:42.12] Muller found that x-rays can also have a deadly effect. When he x-rayed fruit flies, a certain proportion of their descendants died as embryos and the eggs never hatched. [00:36:57.41] Again I suppose a mutation means that something happens in the cell. [00:37:01.41] Have they found out what happens? [00:37:03.31] Scientists who've photographed irradiated cells find that strange things happen. [00:37:09.92] This is a normal cell dividing. The chromosomes split, draw apart, and 2 new cells are formed. [00:37:24.59] These are cells that have been irradiated. They cannot divide normally. Some of the chromosomes are broken, some are misshapen. [00:37:52.51] Sometimes the chromosomes fail to split and the cell cannot reproduce. [00:38:12.17] But lighter doses of radiation may cause changes that can't be seen in the chromosomes, apparently by producing changes in the genes themselves. Thus the descendants of irradiated germ cells give us [00:38:25.05] albino corn, [00:38:27.28] distorted ears of corn, [00:38:29.62] and stunted plants. [00:38:32.53] But, Dr. Baxter, are all the effects of radiation bad? [00:38:36.91] Most of them are, and therefore we must be very careful when we use radiation. But scientists are discovering ways to use artificial mutations for the good of mankind, [00:38:48.94] just like one case, irradiation was used during World War II to produce new strains of the mold which makes penicillin. [00:39:01.33] These artificially created strains increased production of penicillin several times over. [00:39:15.06] Thousands of lives were saved. [00:39:20.58] Radiation is sometimes used to check the abnormal cell division we know as cancer. Cancer cells multiply wildly in an abnormal way. Scientists are trying to find out what has gone wrong. [00:39:43.03] We know that all cells are more easily affected by radiation when they are dividing. That is why cancer cells can sometimes be knocked out by x-ray treatment. [00:39:58.48] But to me the greatest service any science performs, and therefore its most practical aspect, is what it adds to man's fund of knowledge, the knowledge of ourselves and the world we live in. [00:40:11.51] One of the most exciting fields of science today is the continuing search to find and identify those invisible units of heredity that Mendel imagined 100 years ago. [00:40:23.61] Do you think that they'll ever see what those units look like? [00:40:26.14] Well they're getting warm, and the road they're taking is leading them close to the secret of life itself. [00:40:33.72] The first big clue turned up in Switzerland. The scientist, Friedrich Miescher, experimenting with Rhine River salmon discovered unknown chemicals in the salmon's sperm. [00:40:44.82] One of these chemicals was later found to be present in the chromosomes of all kinds of cells, [00:40:51.83] one called deoxyribonucleic acid, known by the letters DNA. [00:41:03.23] Could this complicated substance with the long name be Mendel's particle of heredity, the gene itself? [00:41:10.94] It looks pretty much as if DNA is the material that carries our heredity, and here is an experiment that shows why we think so. This demonstration is by Dr. Harriet Ephrussi-Taylor. [00:41:25.28] About the smallest cells we know of are bacteria, but they too have heredity. [00:41:31.69] We have discovered that some bacteria have become resistant to drugs, to antibiotics. This resistance is hereditary. In other words the bacteria have acquired a mutation for resistance. [00:41:43.14] This is how we can demonstrate what happens. [00:41:48.28] Both ot these plates contain an antibiotic that kills bacteria. [00:41:53.22] This dish has been spread with ordinary pneumococcus bacteria, the kind that causes pneumonia. [00:42:00.22] None of the cells here have grown because the antibiotic has killed them. [00:42:07.45] The second dish has been spread with the same kind of bacteria, except that this strain is resistant. These cells are flourishing. [00:42:18.94] Now we can extract the DNA from the resistant bacteria, and we get these pure fibers of DNA. [00:42:29.28] Here you can see the fibers more clearly. [00:42:34.01] We have put a little of this DNA into a tube. Now we add to it the bacteria which are not resistant and let them grow for a little while. [00:42:45.22] Finally we spread these treated bacteria from the tube on a dish containing the antibiotic, spelling out the letters DNA, and leave it in a warm place for a day. [00:43:05.61] By the next day something surprising has happened. The bacteria have multiplied. Their heredity has been changed. [00:43:14.33] Some of the bacteria we treated have picked up the DNA and from it have gained the ability to resist the drug. [00:43:22.09] What is more, they have passed the resistance along to their descendants. [00:43:27.19] Unbelievable as it seems, we can transfer heredity from one strain to another through the substance of DNA. [00:43:35.66] Well, gee, what kind of stuff is DNA? [00:43:38.89] Remember what we said about seeing a gene? [00:43:43.36] This is a most important photograph, a close up of the DNA molecule, magnified more than 100,000 times. This molecule may be the gene itself. [00:43:58.41] It looks like a tangle of thread. [00:44:00.28] Yes, and the way that molecule looks, long and thread-like, is a key part of our story. [00:44:07.19] Using physical and chemical clues, scientists have been able to figure out how the DNA molecule looks in detail. [00:44:16.12] This concept, one of the most brilliant theories of modern science, was formulated by 2 young men, [00:44:23.47] an American, J.D. Watson, [00:44:26.08] and an Englishman, F.H.C. Crick. [00:44:32.45] This model represents only a short piece of the DNA molecule, magnified many times. [00:44:41.05] It's proportions are deceiving. The DNA molecule is only 1/10,000,000 of an inch in diameter, but the DNA molecules in your body, if laid end to end, would reach to the sun and far beyond, the thread of life. [00:45:00.44] Notice the structure. The pieces are linked together in 2 intertwined chains forming a framework, like a long spiral staircase. The steps of the staircase are of 4 different kinds, [00:45:17.42] 1, [00:45:18.51] 2, [00:45:19.83] 3, [00:45:21.06] 4. [00:45:23.53] We've made models in school. Those balls represent atoms, don't they? [00:45:28.53] Yes, there are 100's of thousands of atoms: [00:45:31.34] Yes, there are 100's of thousands of atoms: carbon, [00:45:33.84] Yes, there are 100's of thousands of atoms: carbon, hydrogen, [00:45:35.38] Yes, there are 100's of thousands of atoms: carbon, hydrogen, oxygen, [00:45:37.11] Yes, there are 100's of thousands of atoms: carbon, hydrogen, oxygen, nitrogen, [00:45:38.47] Yes, there are 100's of thousands of atoms: carbon, hydrogen, oxygen, nitrogen, and phosphorous, [00:45:40.49] Yes, there are 100's of thousands of atoms: carbon, hydrogen, oxygen, nitrogen, and phosphorous, linked together in a fantastic array that spells the living gene. [00:45:45.51] But can you say a bunch of atoms like that are alive? [00:45:48.31] Can they grow? [00:45:49.95] No, but put them all together into a DNA molecule, and in this molecule you have an essential quality of living matter, the ability to reproduce, to make copies of itself. [00:46:02.66] And of all the molecules known to chemistry, only DNA and its relatives have this ability. [00:46:09.58] The theory of Watson and Crick assumes that when a gene is ready to reproduce itself, to divide, as it must do if the chromosomes divide, the whole DNA molecule comes apart in 2 pieces. [00:46:23.86] The twin chains that it's made of unwinding like the strands of a rope. [00:46:29.89] Floating around it in the cell are smaller molecules which make up a sort of spare parts supply for DNA. [00:46:40.81] They are drawn by chemical forces to find open spots to join, forming the steps of the staircase, until each strand of DNA has made itself a new partner, [00:46:51.78] and now 2 double chains, 2 identical molecules, exist where only 1 existed before. [00:46:59.72] This is the theory of how heredity is passed on. Mind you, this is just a theory, but it makes sense. Many scientists are at work trying to see if it is really correct. [00:47:11.56] That's extremely interesting, Dr. Baxter, but there's something I don't understand. You said before, "genes make us different." [00:47:19.50] Yes, and if all genes are made of DNA, why aren't we all alike? [00:47:25.11] You put your finger on an intriguing part of the puzzle. If all DNA molecules are made up of the same parts, how can people differ? [00:47:35.25] The evidence is strong that the 2 interlinked spirals are the same in all creatures, but the difference, which makes you you and me me is to be found on the stair steps of the spiral. [00:47:55.47] There are only 4 kinds of stair steps, but the order in which they are arranged, can be varied enormously from one DNA molecule to another. [00:48:06.16] So it may be the arrangement of the steps in this fantastic stairway that spells out the difference between you and me, [00:48:13.97] between a fish and a bird, [00:48:16.23] between a grasshopper and a redwood tree. [00:48:19.73] Could the sequence of the stair steps be a kind of message to the cell, a genetic code telling it what to do? [00:48:28.84] One combination might be part of the code for producing your curly hair. [00:48:36.62] Another combination might decide that you'll be left-handed, or that you'll inherit a white forelock. [00:48:47.06] The number of possible combinations is fantastic. Millions of such combinations working together could produce the countless complex traits that make up our inheritance. [00:49:06.11] Research on DNA is one of the great new challenges in science. For the young scientists of the future, there are many exciting questions ahead. [00:49:17.12] Can we learn how to read the codes in DNA, how the gene passes its orders along to the rest of the cell, why certain genes work only at certain ages, [00:49:29.56] infancy, [00:49:32.03] childhood, [00:49:34.26] adulthood, [00:49:36.58] and old age. [00:49:41.51] Astronomers tell us there may be millions of planets capable of supporting life. Is DNA a basic chemical of life on other planets, as it is on earth? [00:49:56.59] Someday we may know the answers to these questions, and when we do, science, always pushing forward, will find new mysteries to be solved. [00:50:05.97] For the physical nature of life around us in all its wonderful variety is a constant marvel to mankind. [00:50:25.92] Life reproducing itself in its own likeness provides endless challenges to human curiosity. [00:50:36.59] The power of the human mind to observe, to inquire, to reason, to imagine the existence of particles that are too small to see or things too great to measure, [00:50:51.58] that power of the mind is unlocking the deepest secrets of nature. [00:50:57.48] For the mind is the great lever of all things. Human thought is the process by which human ends are ultimately answered. [00:51:23.25] The Bell System is grateful to the many distinguished scientists who helped to prepare this story of genetics. [00:51:29.89] Our thanks to the advisors who supplied and checked the scientific content [00:51:40.36] and to the individuals and organizations who provided special material. [00:51:48.56] Our thanks to the advisory board which reviews the scientific aspects of these programs. Its members represent the broad range of modern science, [00:51:57.79] biology and genetics, [00:51:59.64] biology and genetics, medicine, [00:52:01.31] biology and genetics, medicine, bacteriology and botany, [00:52:03.78] biology and genetics, medicine, bacteriology and botany, chemistry, [00:52:06.31] geophysics, [00:52:09.12] geophysics, physics, [00:52:10.66] geophysics, physics, anthropology, [00:52:12.16] geophysics, physics, anthropology, electronics and acoustics, [00:52:14.76] mathematics, [00:52:17.56] mathematics, engineering. [00:52:19.33] To all these men the Bell System is indebted for their support of this venture in public education through entertainment. (music) [00:53:03.75] [00:53:29.14]