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The Century of the Gene. Molecular Biology and Genetics GINÉS MORATA

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The Century of the Gene. Molecular Biology and Genetics GINÉS MORATA the century of the gene. molecular biology and genetics GINÉS MORATA The twentieth century was the century in which In the present text, I will deal with the history of human society incorporated technological those scientifi c events that led to this situation and development in a massive way. For much of that briefl y speculate about the implications these new century, the greatest technological contributions discoveries have for future society, and even for our grew out of the physical sciences: automobiles, the own understanding of human nature. telephone, airplanes, plastics, computers, and so on. The introduction of those factors has changed society Turning points in biological knowledge and human behavior more than even political and Over the course of its history, biology has undergone social events. three major revolutions. And here we use the term During the second half of the twentieth century, “revolution” to refer to the emergence of a discovery however, and especially during the last two decades, that is important unto itself but also leads to a radical biological technology with enormous medical and change in the general approach that characterized social potential has emerged. This technology offers this discipline until then. a new image of the evolution of life on our planet The fi rst revolution took place in 1860 with the and is destined to revolutionize the very structure evolutionist theories of Darwin and Wallace, who of human society. defended the universality of the origin of all living Perhaps the person who has most lucidly delved beings. The second revolution was the discovery of the into these ideas is Sydney Brenner. One of the most universality of the biological information mechanism brilliant scientists of the twentieth century, he will be proposed by Watson and Crick in 1953. The third remembered by the history of science for his enormous revolution has been the discovery of the universality contributions to molecular biology, a science he was of animal design and that of the basic processes that decisively involved in creating. Brenner says that new regulate biological functions. This last revolution took biology offers us greater comprehension of ourselves, place in the twentieth century, between 1985 and 2000. and a new understanding of humans as organisms: “… Unlike the previous ones, it is the result of contributions for the fi rst time, we can pose the fundamental problem by a relatively large number of researchers. These three of man and begin to understand our evolution, our events have led to a new understanding of evolution and history, our culture and our biology as a whole.” of the biology of human beings themselves. 162 FRONTIERS OF KNOWLEDGE Evolutionary fact simply one more species among the millions created The idea that species change over time is very old by evolution. It is no surprise that there was a great and certainly earlier than Darwin’s proposal. In the social reaction to this in Darwin’s time. Even now, year 520 B.C., in his treatise, On Nature, Anaximander evolution is not accepted by all members of society. of Miletus introduced the idea of evolution, stating According to the Gallup institute, in 2004, more that life began in the oceans. In his book, Historia than half of the United States believed that man was Plantarum, published in 1686, John Ray catalogs literally created, exactly as the Bible states, some 18,600 types of plants and proposes the fi rst defi nition 10,000 years ago. of species based on common descent. And Darwin’s own grandfather, Erasmus Darwin, explicitly proposed Genetics and evolution: an operational defi nition that animal species change over time. of the gene What differentiates Darwin and Wallace from Darwin offered a descriptive explanation of biological their predecessors is that they proposed a plausible diversity that was plausible, but not mechanistic. The mechanism of evolution based on the idea of natural question is: if all living organisms have a shared origin, selection. Darwin in particular proposed that the strength what biological function is common to all of them, of natural selection lay in the survival of the fi ttest, since transmitted from parents to offspring and modifi able their greater capacity for survival also insured them in order to generate biological diversity? In his time, a greater capacity to transmit their characteristics to Darwin was unable to answer these questions. It was their progeny. Through this process, the characteristics precisely the posing of such questions that led to of populations of each particular species were gradually Genetics, the discipline that studies how biological modifi ed over the course of successive generations. information is transmitted and modifi ed. We owe the Darwin also had access to information unknown fi rst evidence of the existence of inheritable genetic to his predecessors, and that information contributed information to Gregor Mendel, an Augustinian monk considerably to his comprehension of the evolutionary who demonstrated that the shape or color of peas is phenomenon. It was known, for example, that the Earth faithfully transmitted from one generation to the next. was much older than had previously been thought, But the progress of Genetics in the twentieth which allowed much more time for the gradual change century owes much to the fruit fl y, Drosophila prophesized by the theory of natural selection. By melanogaster, an organism that has become a classic Darwin’s time, there was also a very well cataloged object of study for genetic research because it roster of fossils, which made it possible to verify the breeds easily in laboratory settings, has a very short existence of gradual change in many lines of animals biological cycle (which is very useful when studying and plants. This clearly supported Darwin’s proposal. the transmission of diverse traits from one generation It was also known that artifi cial selection is able to to the next) and is totally innocuous to human generate very profound morphological changes in a beings. Drosophila studies revealed many concrete very short period of time. That becomes clear when inheritable traits (genes), demonstrating that we consider, for example, the vast variety of breeds of they are located and aligned in cell nucleae—in dogs now in existence. They all derive from the wolf, organules called chromosomes—and that each gene but over the course of fi ve to ten thousand years of is situated in a specifi c position in the chromosome. artifi cial—not natural—evolution, man has managed to They also showed that inheritable variations create a great diversity of canine breeds. This indicates (mutations) naturally appear in genes, and that the degree to which biological material is versatile these mutations are the source of the biological when subjected to selection. variation that is essential to the evolutionary process. If we were to summarize the implications of These mutations can also be artifi cially induced evolutionary theory, we would concentrate on three using radiation or chemical compounds. In sum, points: 1) all living beings have a shared origin; 2) what Drosophila genetics discovered is that the real there has been a process of gradual change over many motivating force for evolution are the genes, which millions of years that has led to all biological diversity make up the inheritable genetic information, and on this planet; and fi nally, 3) the human species is which can be modifi ed. simply one more of the hundreds of thousands of After over a century of research on this fl y, knowledge species that exist or have existed. Darwin’s proposal of its genetics is the most complete of all the animal refl ects a Copernican change in the approach to the kingdom, and a series of concepts and technologies have position of the human species as a biological entity. been developed to carry out experiments that are not Man is no longer the center of creation. Instead, he is possible with any other species. 163 THE CENTURY OF THE GENE GINÉS MORATA DNA ARN PROTEINS Fundamental biological functions: Total information Individual message 3,000 basic functions (Sequence of 4 bases) (Sequence of 4 bases) + 10–30,000 specifi c ones (Sequence of 20 amino acids) The message of the ADN - GUC - AAG - GCA - AGC - CUA - AGA - it’s translated in an specifi c secquency - Val - Lys - Ala - Ser - Leu - Arg - of amino acids formed by the different proteins of the body. The translation code, called “Genetic Code,” is universal for all organisms Figure 1. Translation of the genetic text. The nature of genetic information and the sequence of the Drosophila fruit fl y contains The problem that arose after that, around the nineteen 120 million pares of bases, while the human sequence forties, was to discover the gene’s physical nature. has no less than 3,300 million pairs of bases. Each of What was its chemical composition? The solution to these sequences represents a sort of formula for the this problem led to what I call the second revolution in construction of the species in question. biology: Watson and Crick’s explanation of the nature and structure of genetic information as DNA. The A universal genetic code famous article published in Nature magazine in 1953 The problem is that life processes are not catalyzed by was the beginning of a biological revolution destined to DNA, but instead by proteins. DNA is simply a recipe that change the very course of humanity. DNA is a molecule has to be translated into the full variety of proteins— with a double-helix structure consisting of two large some 3,000 basic ones—that control life processes, chains of molecules of a sugar (deoxy-ribose) linked including the replication and expression of DNA itself.
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