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MOST IMPORTANT SCIENTIFIC DISCOVERIES
Fundamentals of genetics. History and essence of scientific discovery
Directory / The most important scientific discoveries It took mankind more than 2500 years to be able to uncover the patterns of heredity. "... Ancient natural philosophers and doctors could not correctly understand the phenomena of heredity due to the limited and partially erroneous knowledge of the anatomy and physiology of the organs of reproduction and the processes of fertilization and even development," notes the well-known Soviet geneticist A.E. Gaisinovich. "They had the most accessible study structures of animals, and it is not surprising that they transferred to humans the features of the anatomy of their genital organs found in animals ... The origin of the male seed was unknown in antiquity, and this led to the creation of erroneous ideas about the formation of the seed from particles separated by all organs of the body and repeating their shape and structure in miniature. It was, in fact, the first theory of heredity, which showed extraordinary vitality until the XNUMXth century, when it was revived by Charles Darwin in his hypothesis of pangenesis ... "Two points of view fought. The first, which allowed the existence of the female seed and its participation in fertilization. And the second, one of the brightest representatives of which was Aristotle. He believed that the shape of the future embryo is determined only by the male seed. Epigenetic theory development of Aristotle and the theory of pangenesis and preformation have undergone centuries of struggle. “Revived in the XNUMXth century by W. Harvey,” writes A.E. Gaisinovich, “nevertheless, it was rejected by most biologists based on the observations of microscopists of the XNUMXth–XNUMXth centuries. Only in the second half of the XNUMXth century was the doctrine of preformation shaken and new ones were made. attempts to formulate epigenetic theories of development and heredity based on the recognition of the existence of male and female seeds and the principle of pangenesis (P. Maupertuis, J. Buffon).Although K.F. Wolf managed to lay the first foundations of embryology, however, knowledge of the essence of fertilization processes remained hidden from him , and his ideas about the phenomena of variability and heredity were premature and erroneous. A great step forward in the study of the phenomena of heredity was the use of plants for experiments on their hybridization. The experiments of hybridizers of the XNUMXth century finally confirmed the presence of two sexes in plants vaguely assumed in antiquity and their equal participation in the phenomena of heredity (I. Ke Lreiter and many others). However, the doctrine of the immutability of species and its imaginary confirmation during interspecific hybridization did not allow them to reliably prove the independent transmission of individual species and individual traits by inheritance. This was a great merit of the monk-scientist Gregor Mendel, rightfully considered the founder of the science of heredity. Gregor Johann Mendel (1822–1884) was born in Heisendorf in Silesia to a peasant family. In elementary school, he showed outstanding mathematical abilities and, at the insistence of his teachers, continued his education at the gymnasium in the small nearby town of Opava. However, there was not enough money in the family for the further education of Mendel. With great difficulty they managed to scrape together to complete the gymnasium course. The younger sister Teresa came to the rescue: she donated the dowry accumulated for her. With these funds, Mendel was able to study for some more time at university preparation courses. After that, the family's funds dried up completely. The way out was proposed by professor of mathematics Franz. He advised Mendel to enter the Augustinian monastery in Brno. It was headed at that time by Abbot Cyril Napp, a man of broad views who encouraged science. In 1843, Mendel entered this monastery and received the name Gregor (at birth he was given the name Johann). Four years later, the monastery sent the twenty-five-year-old monk Mendel as a teacher to a secondary school. Then, from 1851 to 1853, he studied natural sciences, especially physics, at the University of Vienna, after which he became a teacher of physics and natural science at a real school in the city of Brno. His teaching activity, which lasted fourteen years, was highly appreciated by both the leadership of the school and the students. According to the memoirs of the latter, Mendel was one of the most beloved teachers. For the last fifteen years of his life, Mendel was the abbot of the monastery. From his youth, Gregor was interested in natural science. More of an amateur than a professional biologist, Mendel was constantly experimenting with various plants and bees. In 1856 he began the classic work on hybridization and analysis of the inheritance of traits in peas. Mendel worked in a tiny monastery garden, less than two and a half acres. He sowed peas for eight years, manipulating two dozen varieties of this plant, different in flower color and seed type. He did ten thousand experiments. Studying the shape of seeds in plants obtained as a result of crossings, in order to understand the patterns of transmission of only one trait ("smooth - wrinkled"), he analyzed 7324 peas. He examined each seed with a magnifying glass, comparing their shape and making notes. Mendel formulated the purpose of this series of experiments in the following way: “The task of the experiment was to observe these changes for each pair of differing traits and to establish the law by which they pass in successive generations. Therefore, the experiment is divided into a number of separate experiments according to the number of constant -distinguishing features. With Mendel's experiments, another countdown began, the main distinguishing feature of which was Mendel's again introduced hybridological analysis of the heredity of individual traits of parents in offspring. But it was precisely this that allowed the modest teacher of the monastic school to see a complete picture of the study; to see it only after having had to neglect the tenths and hundredths due to the inevitable statistical variations. Only then did the alternative traits literally "marked" by the researcher reveal something sensational to him: certain types of crossing in different offspring give a ratio of 3:1, 1:1, or 1:2:1. Mendel turned to the work of his predecessors for confirmation of a hunch that had flashed through his mind. Those whom the researcher considered to be authorities came at different times, and each in his own way, to a general conclusion: genes can have dominant (suppressive) or recessive (suppressed) properties. And if so, Mendel concludes, then the combination of heterogeneous genes gives the very splitting of features that is observed in his own experiments. And in the very ratios that were calculated using his statistical analysis. "Checking the harmony of algebra" of the ongoing changes in the resulting generations of peas, the scientist introduces letter designations. He capitalizes the dominant and lowercase the recessive state of the same gene. Multiplying combination series. (A+2Aa+a)x(B-2Bb+b), Mendel finds all possible types of combination. “The series, therefore, consists of 9 members, of which 4 are represented in it once each and are constant in both characters; the forms AB, ab are similar to the original species, the other two represent the only possible constant combinations between the combined characters A. , a, B, b. Four terms occur twice each and are constant in one character, hybrid in another. One term occurs 4 times and is hybrid in both characters... This series is undoubtedly a combinational series in which term by term, both series of development for characters A and a, B and b." As a result, Mendel comes to the following conclusions: “The descendants of hybrids that combine several significantly different traits are members of a combination series in which the development rows of each pair of differing traits are connected. This simultaneously proves that the behavior in a hybrid combination of each pair of differing traits is independently from other differences in both original plants", and therefore "constant characters that occur in various forms of a related plant group can enter into all compounds that are possible according to the rules of combinations". Summarized, the results of the scientist's work look like this: 1) all hybrid plants of the first generation are the same and show the trait of one of the parents; 2) among hybrids of the second generation, plants appear with both dominant and recessive traits in a ratio of 3: 1; 3) two characters in the offspring behave independently in the second generation. 4) it is necessary to distinguish between traits and their hereditary inclinations (plants exhibiting dominant traits may latently bear the makings of recessive traits); 5) the association of male and female gametes is random in relation to the inclinations of what characters these gametes carry. In February and March 1865, in two reports at meetings of the provincial scientific circle, called the Society of Naturalists of the city of Brno, one of its ordinary members, Gregor Mendel, reported on the results of his many years of research completed in 1863. Despite the fact that his reports were rather coldly received by the members of the circle, he decided to publish his work. She saw the light in 1866 in the writings of a society called "Experiments on plant hybrids." Contemporaries did not understand Mendel and did not appreciate his work. Too simple, unsophisticated seemed to them a scheme in which, without difficulty and creaking, complex phenomena, which, in the minds of humanity, were the foundation of an unshakable pyramid of evolution, fit in. In addition, there were vulnerabilities in Mendel's concept. So, at least, it seemed to his opponents. And the researcher himself, too, because he could not dispel their doubts. One of the "culprits" of his failures was a hawk. Botanist Karl von Naegeli, a professor at the University of Munich, having read Mendel’s work, suggested that the author test the laws he discovered on the hawkweed. This small plant was Naegeli's favorite subject. And Mendel agreed. He spent a lot of energy on new experiments. Hawkweed is an extremely inconvenient plant for artificial crossing, since it is very small. I had to strain my vision, but it got worse and worse. The offspring resulting from the crossing of the hawkweed did not obey the law, as he believed, to be correct for everyone. Only years later, after biologists established the fact of other, non-sexual reproduction of the hawksbill, the objections of Professor Naegeli, Mendel's main opponent, were removed from the agenda. But neither Mendel nor Nägeli himself, alas, were alive anymore. Very figuratively, the greatest Soviet geneticist Academician B.L. Astaurov: "The fate of Mendel's classical work is perverse and not alien to drama. Although he discovered, clearly showed and to a large extent understood very general laws of heredity, the biology of that time had not yet matured to realize their fundamental nature. Mendel himself with amazing insight foresaw the universal significance of those discovered on peas and received some evidence of their applicability to some other plants (three types of beans, two types of levkoy, corn and night beauty).However, his persistent and tedious attempts to apply the found patterns to the crossing of numerous varieties and species of hawk did not justify hopes and suffered a complete fiasco "How happy was the choice of the first object (peas), just as unsuccessful was the second. Only much later, already in our century, it became clear that the peculiar patterns of inheritance of traits in a hawk are an exception that only confirms the rule. In Mendel's time, no one could to ripen that the crossings of hawkweed varieties undertaken by him did not actually occur, since this plant reproduces without pollination and fertilization, in a virgin way, through the so-called "apogamy". The failure of painstaking and strenuous experiments, which caused an almost complete loss of vision, the burdensome duties of a prelate that fell on Mendel and advanced years forced him to stop his favorite studies. Glory and honor will come to Mendel after death. He will leave life without unraveling the secrets of the hawk, which did not "fit" into the laws of uniformity of hybrids of the first generation and the splitting of signs in the offspring that he derived. Too early the great explorer reported his discoveries to the scientific world. The latter was not yet ready for this. Only in 1900, having rediscovered Mendel's laws, the world was amazed at the beauty of the logic of the researcher's experiment and the elegant accuracy of his calculations. And although the gene continued to be a hypothetical unit of heredity, doubts about its materiality finally disappeared. The revolutionary role of Mendelism in biology became more and more obvious. By the early thirties of our century, genetics and the laws of Mendel underlying it had become the recognized foundation of modern Darwinism. Mendelism became the theoretical basis for the development of new high-yielding varieties of cultivated plants, more productive breeds of livestock, useful types of microorganisms. He also gave impetus to the development of medical genetics. famous physicist Erwin schrödinger believed that the application of Mendel's laws is tantamount to the introduction of the quantum principle in biology Author: Samin D.K.
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