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MOST IMPORTANT SCIENTIFIC DISCOVERIES
Chromosomal theory of heredity. History and essence of scientific discovery
Directory / The most important scientific discoveries In 1900, independently of each other, three botanists - K. Korrens (Germany), G. de Vries (Holland) and E. Chermak (Austria) discovered patterns previously discovered by Mendel in their experiments. Then, having come across his work, they republished it in 1901. This contributed to a deep interest in the quantitative laws of heredity. By that time, cytologists had discovered material structures whose role and behavior could be uniquely linked to Mendelian patterns. A similar connection was seen in 1903 by W. Setgon. We received a substantiation of Mendel's views on hereditary factors, on the presence of a single set of factors in gametes and a double set in zygotes. A year earlier, T. Boveri presented evidence in favor of the participation of chromosomes in the processes of hereditary transmission. He showed, for example, that the normal development of a sea urchin is possible only if all chromosomes are present. By establishing the fact that it is chromosomes that carry hereditary information, Setton and Boveri laid the foundation for a new direction in genetics - the chromosome theory of heredity. The decisive contribution to the development of this theory was made by the American scientist Morgan. Thomas Gent Morgan (1866–1945) was born in Lexington, Kentucky. His father was Charlton Gent Morgan, the US Consul in Sicily and a relative of the famous magnate J. P. Morgan. From childhood, Thomas showed an interest in natural history. He entered the University of Kentucky and graduated in 1886. In the summer immediately after his graduation, he went to the naval station at Ennisquam on the Atlantic coast, north of Boston. Here Thomas first got acquainted with the marine fauna. This acquaintance captured him, and from then on the study of marine forms attracted his special interest throughout his life. He did his graduate work under the guidance of William Keith Brooks, a marine biologist. In 1888, Morgan moved to Woods Hole, and in the summer of that year he began working at the State Fishing Station. However, in 1890, Thomas returned to Woods Hole at the Marine Biological Station, and spent the rest of his life mostly summering here. In the same year, Morgan succeeded as department head at Brian Mawr College. In 1897 he was elected one of the trustees of the maritime station, and he remained so all his life. That was the year the station and its administration were taken over by the Young Turks, and Morgan was one of the new trustees chosen at this critical period. At the same time, Wilson from the University of Chicago appeared at the station. It was Wilson who, in 1904, persuaded him to take up a professorship at Columbia University. For twenty-four years they worked in very close association. Like most zoological biologists of his time, Morgan was educated in comparative anatomy and especially descriptive embryology. His dissertation dealt with the embryology of a species of sea spider and was based on material he collected at Woods Hole. This work was based on descriptive embryological data with conclusions extending into the realm of phylogeny. Morgan had an early interest in experimental embryology. The problems that Morgan and other embryologists were then working to solve concerned the extent to which development depends on or is influenced by specific formative substances supposedly present in the egg. How such formative substances are involved in development and how they function. The young scientist was also engaged in physiological research. But genetics brought him real fame. At the end of the nineteenth century, Morgan visited the garden of Hugh de Vries in Amsterdam, where he saw the defrizian lines of evening primrose. It was then that he showed his first interest in mutations. Whitman, director of the Biostation at Woods Hole, who was an experimental geneticist, also played a role in Morgan's reorientation. He devoted many years to the study of hybrids between different species of doves and pigeons, but did not want to apply the Mendelian approach. This is understandable, since the pigeons in this case get, to put it mildly, a hodgepodge. Strange signs that do not give a beautiful ratio of 3: 1 confused Morgan as well. For the time being, he saw no way out. Thus, before 1910, Morgan could rather be considered an anti-Mendelist. In that year, the scientist began to study mutations - inherited changes in certain signs of the body. Morgan conducted his experiments on Drosophila, small fruit flies. With his light hand, they have become a favorite object of genetic research in hundreds of laboratories. They are easy to find and are found everywhere. They feed on plant sap, any fruit rot. Their larvae feed on bacteria. The reproduction energy of Drosophila is huge: from an egg to an adult - ten days. For geneticists, it is also important that Drosophila are subject to frequent hereditary changes. They have few chromosomes - only four pairs. The cells of the salivary glands of fly larvae contain giant chromosomes, which are especially convenient for research. With the help of the fly, genetics has made many discoveries to date. The popularity of Drosophila is so great that a yearbook dedicated to it is published in English, containing abundant and varied information. Having started his experiments, Morgan first obtained fruit flies in grocers and fruit shops, since the shopkeepers, who were annoyed by the flies, willingly allowed the eccentric to catch them. Then, together with his coworkers, he began to breed flies in his laboratory, in a large room, dubbed "fly". It was a thirty-five-square-meter room with eight work stations. There was a place where they cooked food for flies. There were usually at least five workers in the room. “I’m afraid I won’t be able to give an idea of the atmosphere that prevailed in the laboratory,” recalled one of the associates of the scientist Alfred Sturtevant. “I think it was something that you need to experience in order to fully appreciate. One of the biggest advantages of this place was the presence both Morgan and Wilson. So students specializing in one of them saw the other very often. They complemented each other in a number of ways and were great friends. In the early years at Columbia University, we fed bananas to Drosophila, and in the corner there was always a big bunch of bananas hanging in the room. Wilson's room was a few doors down the corridor from ours. He was very fond of bananas, so there was another motivating reason to visit the "fly room" often. Throughout this time, Morgan made regular visits to Woods Hole. This, however, did not mean a break in experiments with Drosophila. All cultures were packed in casks - large casks of sugar, and sent by express steamer. What you started in New York, you ended up in Hole and vice versa. We always came by water: that was the time when the Fall River Line was in operation, and Morgan was always doing all sorts of experiments that had nothing to do with work on Drosophila. He raised chickens, rats and mice, grew various plants. And it was all carried by hand, and loaded onto the Fall River Line ship, and then brought back to New York. And when Morgan got here, he plunged headlong into working with marine forms, into the embryology of one variety or another, even though work with Drosophila was actively moving forward in the meantime. Such was the Morgan style of work - he did not feel happy if he did not forge several things from the hot at the same time. are in chromosomes, it was possible to answer the question whether the numerical regularities established by Mendel? Mendel quite rightly believed that such regularities would be true if and only if the studied factors were combined independently of each other in the formation of zygotes. Now, on the basis of the chromosome theory of heredity, it should be recognized that this is possible only when the genes are located on different chromosomes. But since the number of the latter is small compared to the number of genes, it was to be expected that genes located on the same chromosome would pass from gametes to zygotes together. Therefore, the corresponding traits will be inherited by groups. This assumption was verified by Morgan and his collaborators K. Bridges and A. Sturtevant. Soon, a large number of various mutations were discovered in Drosophila, that is, forms characterized by various hereditary characteristics. In normal, or, as geneticists say, wild-type fruit flies, the body color is grayish-yellowish, the wings are gray, the eyes are dark brick red, the setae covering the body and the veins on the wings have a well-defined arrangement. In the mutant flies that were found from time to time, these signs were changed: the body, for example, was black, the eyes were white or otherwise colored, the wings were rudimentary, etc. Some individuals carried not one, but several mutations at once: for example, a fly with a black body could , moreover, possess rudimentary wings. The variety of mutations allowed Morgan to start genetic experiments. First of all, he proved that genes located on the same chromosome are transmitted together during crossings, that is, they are linked to each other. One linkage group of genes is located on one chromosome. Morgan also received strong confirmation of the hypothesis of the linkage of genes in chromosomes in the study of the so-called sex-linked inheritance. By determining that the Drosophila eye color gene is located on the X chromosome, and by following the behavior of the genes in the offspring of certain males and females, Morgan and his collaborators obtained strong support for the gene linkage hypothesis. For outstanding work in the field of genetics, Morgan was awarded the Nobel Prize in 1933. In the thirties Vavilov wrote: "The laws of Mendel and Morgan formed the basis of modern scientific ideas about heredity, on which breeding work is built, both with plant and animal organisms ... Among biologists of the XNUMXth century, Morgan stands out as a brilliant experimental geneticist, as a researcher of an exceptional range ". Author: Samin D.K.
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