How a fly replaced a pea, why scientific discoveries turned out to be more interesting than the presentation of the Nobel Prize, and how an honorary member of the USSR Academy of Sciences was treated exclusively in a negative context, read in the section “How to get a Nobel Prize.”
I heard the name of our hero as a child, and in a clearly negative context. There weren’t as many books then as there are now, and I read everything I could get my hands on. And somehow I came across a certain novel about Soviet Armenia in the 1940s and 50s (by the way, a very good plot). Of course, there was a collective farm, and in it, of course, there were record-breaking cows that “beat bourgeois cows, such Weismann-Morganists.” Well, at that time there were the times of Comrade, and the surname of Thomas Hunt Morgan, one of the founders of genetics, could only be a negative common noun.
And this despite the fact that this most negative character has been a foreign corresponding member of the USSR Academy of Sciences since 1923, and since 1932 an honorary member of the Soviet Academy of Sciences. The fact that a year later he became a Nobel laureate could be attributed to the machinations of the bourgeois world, which has always oppressed domestic scientists (see article about). Fortunately, those days are long gone. Therefore, we will boldly tell the scientific biography of a man who made a serious breakthrough in understanding how life works, without ideological assessment. So, Thomas Hunt Morgan.
Thomas Hunt Morgan
Wikimedia Commons
Thomas Hunt Morgan
Nobel Prize in Physiology or Medicine 1933. Formulation of the Nobel Committee: “For discoveries related to the role of chromosomes in heredity”
Through his mother, Morgan is the great-grandson of Francis Scott Key himself - American Mikhalkov and El-Registan in one bottle. He was a lawyer, a poet, and the author of the poem "The Defense of Fort McHenry" (1814), an excerpt from which - "The Star-Spangled Banner" - was set to a British drinking tune and became the official US anthem in 1931. Morgan still managed to witness the triumph of his great-grandfather's creation.
Francis Scott Key
Wikimedia Commons
His father, Charlton Hunt Morgan, was a diplomat, but the first-born (there were three children in the family) did not follow in his father’s footsteps. Morgan's biographers write that during his summer vacation, the future geneticist scoured the rural areas of Kentucky, collecting fossils (there was a real boom in amateur paleontology in the second half of the 19th century). Thus began Thomas' path to what is now called Life Sciences. He received his bachelor's degree from Kentucky State College. It was there that Morgan became acquainted with Darwin's theory, but continued to study almost pure biology.
At Johns Hopkins University, where the future Nobel laureate entered in 1887, he studied physiology, animal morphology and embryology. Morgan received his doctorate for studying the embryology of sea spiders. And if he, like many scientists of those years, was exclusively engaged in this, it is unlikely that we would have heard the name Morgan outside the context of “gentlemen of fortune.” For quite a long time, more than 15 years, Thomas Hunt Morgan was engaged in experimental embryology; his works were devoted to the connection between regeneration and early embryonic development. But questions of inheritance still arose. However, at that time practically nothing was known about genetics and heredity.
Everything changed in 1900, when the results of research almost half a century ago, obtained 16 years ago by a deceased monk experimenting on peas in the monastery garden, were introduced into science. The monk's name was Gregor Johann Mendel. His article “Experiments on plant hybrids” was published back in 1866 in the journal Verhandlungen des naturforschenden Vereins Brünn(Proceedings of the Brno Natural History Society), but until 1900 almost no one read it. The beautiful relationships obtained by Mendel have entered science; now all that remains is to explain them.
Gregor Mendel
Wikimedia Commons
Morgan got into the game. Mendel himself called something responsible for certain characteristics “factors”. In the 20th century they began to be called “genes”. In 1902, William Sutton, an American biologist, suggested that genes are located either inside or on the surface of certain structures of the cell nucleus - chromosomes. However, all this was just speculation. It must be said that Morgan was skeptical about Sutton’s idea. As an embryologist, he adhered to the theory that chromosomes are some early product of cell development. It was a matter of material for experiments.
Peas are good, but they take a long time to grow, it takes a long time to accumulate good statistics, and they have as many as 14 chromosomes. A different material was required: quickly multiplying, cheap, with a small number of chromosomes and heritable characteristics. The work of William Castle, a Harvard scientist, came to the rescue; (Drosophila melanogaster).
Charles Woodworth
Wikimedia Commons
This option turned out to be ideal for geneticists. Judge for yourself - only four pairs of chromosomes, it is easy to distinguish a female from a male, 12 days after birth it produces offspring of 1000 individuals. The dream of a biologist who needs to accumulate statistics. Morgan and his team began experiments in 1908. It quickly became clear: yes, chromosomes are the carriers of genes. And genes are really something material that has its place in the chromosome. In a good way, this was already the first step towards the discovery of DNA.
The next step was the observation: Mendel’s beautiful relationships are not always observed. Some traits seem to be linked to each other and are inherited in combination. That is, a combination of two traits can occur in descendants much more often than required by the Mendelian ratio. Morgan draws a logical conclusion: “linked” genes are located nearby and on the same chromosome. He discovered four such groups of genes - corresponding to four pairs of chromosomes. This was the next step in understanding the work of the genetic apparatus and heredity.
Drosophila melanogaster
Wikimedia Commons
However, in 1912, employees who had recently joined Morgan, Alfred Sturtevant (who had already shown in 1911 that the degree of linkage of genes is inversely proportional to the distance between them on the chromosome) and Calvin Bridges, greatly surprised the boss. They found that “linked” genes are inherited together less often than might be expected. This is how crossing over was discovered - the phenomenon of chromosome recombination, when chromosomes in a pair can split and exchange genetic material (however, the physical interweaving of chromosomes itself was discovered back in 1909 by the Belgian cytologist Frans Alfons Janssens).
- 45.29 KbFEDERAL EDUCATION AGENCY
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Khasanova Alina Albertovna
"Thomas Morgan, Contributions to Biology"
Written by: Khasanova A. A.
Introduction
1. Biography of the scientist
2. Early works of T. Morgan
3. Morgan front sight
4. Formation of the chromosomal theory of heredity
Conclusion
Literature
INTRODUCTION
In the thirties of the last century, N.I. Vavilov wrote: “The laws of Mendel and Morgan formed the basis of modern scientific ideas about heredity, on which breeding work with both plant and animal organisms is based... Among the biologists of the 20th century, Thomas Hunt Morgan (1866-1945) stands out - American biologist, one one of the founders of genetics, foreign corresponding member of the Russian Academy of Sciences (1923) and foreign honorary member of the USSR Academy of Sciences (1932), president of the US National Academy of Sciences (1927-31), a brilliant experimental geneticist, researcher of an exceptional range.” The work of Morgan and his school (Herman Joseph Moeller, Alfred Henry Sturtevant and others) substantiated the chromosomal theory of heredity; The established patterns of gene arrangement on chromosomes contributed to the elucidation of the cytological mechanisms of Gregor Mendel's laws of Mendel and the development of the genetic foundations of the theory of natural selection. Received the Nobel Prize in 1933.
1. BIOGRAPHY
Thomas Gent Morgan was born September 25, 1866 in Lexington, Kentucky. His father Charlton Gent Morgan, the US consul in Sicily, was a relative of the famous tycoon J.P. Morgan, mother - Ellen Kay Morgan. Since childhood, Thomas showed an interest in natural history. He entered the University of Kentucky and graduated in 1886. The summer immediately after graduation, he went to the Ennisquam naval station on the Atlantic coast, north of Boston. This was the last year of the local laboratory's existence (2).
The following year, the group that organized and directed this laboratory came to Woods Hole. In Ennisquam, Thomas first became acquainted with marine fauna. This acquaintance captivated him, and from then on the study of marine forms attracted his special interest throughout his life.
He did his graduate work under the supervision of William Keith Brooks, a marine biologist. Brooks was an excellent teacher who trained a whole generation of outstanding American zoologists. In 1888, Morgan moved to Woods Hole, and in the summer of that year he began working at the State Fisheries Station. In 1890, Thomas returned to Woods Hole to the Marine Biological Station, and throughout the subsequent years of his life he spent most of his summers here. That same year, Morgan succeeded Brian Mawr College as department head. In 1897 he was elected one of the trustees of the naval station, and remained so all his life. That was the year the station and its management were taken over by the Young Turks, and Morgan was one of the new trustees elected at this turning point. At the same time, Wilson from the University of Chicago appeared at the station (4).
It was Wilson who convinced him to take a professorship at Columbia University in 1904. For twenty-four years they worked in very close communication.
Like most biologists-zoologists of that time, Morgan was educated in the field of comparative anatomy and especially descriptive embryology. His dissertation concerned 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 inferences extending into the realm of phylogeny.
Morgan, like some of his contemporaries at Johns Hopkins University, was strongly influenced by H. Newell Martin, who was a physiologist and student of T.H. Huxley. It was probably from him that Morgan acquired his penchant for physiological approaches to biology. He developed an early interest in experimental embryology (5). Morgan spent two summers at the Naples Biological Station, where he first went in 1890 and then in 1895. Here he met and became friends with many of those who contributed to the development of experimental embryology: Driesch, Boveri, Dorn and Herbst. Although Morgan was already an experimental embryologist himself, it was this communication that truly directed his interests in this direction. They formed a group of researchers very active both abroad and in the United States. It was an exciting time, since scientists had a new approach to everything and new questions constantly arose.
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 presumably present in the egg. How are such formative substances involved in development and how do they function? The young scientist was also involved in physiological research, but it was genetics that brought him real fame.
At the end of the 11th century, Morgan visited the garden of Hugo de Vries in Amsterdam, where he saw the Defries lines of evening primrose. It was then that he first became interested in mutations. The director of the Woods Hole biological station, Whitman, who was an experimental geneticist, also played a role in Morgan’s reorientation. He devoted many years to studying hybrids between different species of doves and pigeons, but did not want to apply the Mendelian approach. This is understandable, since in this case the pigeons end up with, to put it mildly, a mess. Strange signs that did not give a beautiful 3:1 ratio confused Morgan, and for the time being he did not see a way out.
Thus, before 1910, Morgan could rather be considered an anti-Mendelian. That year, the scientist began studying mutations - inherited changes in certain characteristics of the body.
Morgan conducted his experiments on Drosophila (4), small fruit flies. With his light hand, they became a favorite object of genetic research in hundreds of laboratories. They are easy to get, they are found everywhere, feed on plant sap, all sorts of fruit foulbrood, and the larvae absorb bacteria. The reproductive energy of fruit flies is enormous: it takes ten days from egg to adult. It is also important for geneticists 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; they are especially convenient for research.
With the help of the fly, genetics has now made many discoveries. The popularity of Drosophila is so great that a yearbook dedicated to it is published in English, containing a wealth of varied information (2).
When Morgan began his experiments, he first obtained fruit flies in grocery and fruit shops, fortunately the shopkeepers, who were annoyed by the flies, willingly allowed the eccentric to catch them. Then he and his staff began breeding flies in his laboratory, in a large room dubbed the “fly room.” It was a thirty-five square meter room with eight work stations. They also cooked food for flies there. There were usually at least five workers in the room.
It is now clear that Morgan's experimental technique was simply inadequate to detect the increase in mutation rates that would have occurred under the influence of radium. Nevertheless, the scientist received mutations, began to study them, and everything further stemmed from these supposedly spontaneous mutations. The first of these mutations, not the first to be found, but the first that really made a big difference, was the trait of white eyes, which turned out to be sex-linked. This was a major discovery.
Since 1911, Morgan and his associates began to publish a series of works in which they experimentally, based on numerous experiments with Drosophila, proved that genes are material particles that determine hereditary variability, and that their carriers are the chromosomes of the cell nucleus (5). It was then that the chromosomal theory of heredity was formulated in basic terms, confirming and strengthening the laws discovered by Mendel.
One of the scientist’s associates, Alfred Sturtevant, recalled: “I’m afraid that I will not be able to give an idea of the atmosphere that reigned in the laboratory. I think it was something that had to be experienced to be fully appreciated. One of the greatest advantages of this place was the presence of both Morgan and Wilson. So students specializing in one of them very often saw the other. They complemented each other in a number of ways and were great friends. In our early years at Columbia University, we fed fruit flies bananas, and there was always a big bunch of bananas hanging in the corner of the room. Wilson's room was a few doors down the corridor from ours. He loved bananas very much, so there was another incentive to often visit the “fly room”.
During all this time, Morgan regularly came to Woods Hole. This, however, did not mean a break in experiments with fruit flies. All cultures were packed in barrels - large barrels of sugar, and sent by express steamer. What you started in New York, you ended in Hole, and vice versa. We always came by water - this was the time when the Fall River Line was in operation, and Morgan was always engaged in all sorts of experiments that had nothing to do with work on fruit flies. He raised chickens, rats and mice, and grew various plants. And all of this was 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, in the embryology of this or that variety, even despite the fact that work with Drosophila was in the meantime actively moving forward. This was Morgan’s style of work - he did not feel happy if he did not forge several hot things at the same time” (9).
Morgan came from an aristocratic family, but was devoid of any arrogance or snobbery.
When the Russian scientist Nikolai Vavilov came to Morgan, he was well aware of the work of the Columbia laboratory. It seemed unlikely to Vavilov that genes could be located on a chromosome like beads on a string, and such a concept seemed mechanistic to him.
Vavilov expressed all this to Morgan, expecting sharp, even perhaps arrogant, objections from the world-famous geneticist. Nikolai Ivanovich, of course, could not know the character traits of the famous scientist. After listening carefully to Vavilov, Morgan suddenly said that he himself somehow did not like the idea that genes are located linearly on a chromosome. If anyone gets evidence that this is not so, he will readily accept it.
Was there an inherent amount of hidden irony in this answer from Morgan, because the American loved to tease, loved to play. One of his scientist friends admitted that he often argued with Morgan, but every time he began to think that his arguments had prevailed, he suddenly discovered that, without understanding how this happened, he was arguing from the opposite, losing side . This is how the brilliant scientist knew how to arrange it.
But on the other hand, Morgan was always friendly, always ready to help, and if you wanted to seriously discuss anything with him, be it scientific or personal issues, he was always ready to provide support.
In 1928, Morgan moved to the California Institute of Technology in order to organize a new biology department. What interested him in this enterprise was the opportunity to organize a department as he wanted, and, moreover, in an institute where physics and chemistry were at their best, where a research atmosphere reigned and where work with students was aimed at growing them into researchers (8). Morgan remained at the institute until his death, but he returned regularly to Woods Walk every summer. Over the course of ten years, Morgan's students managed to study three hundred generations of fruit flies.
In the thirties, Vavilov wrote: “Mendel’s and Morgan’s laws formed the basis of modern scientific ideas about heredity, on which breeding work is based, both with plant and animal organisms... Among biologists of the 20th century, Morgan stands out as a brilliant experimental geneticist, as a researcher of exceptional range.”
Morgan died on December 4, 1945.
2. MORGAN'S EARLY WORK
Thomas Hunt Morgan had an interest in natural history and the exact sciences from childhood; During the summer holidays, he enthusiastically explored the countryside, finding and bringing home fossils, and amassed a collection of various species of birds. He later spent two summers conducting geological and biological surveys in the Kentucky mountains while working on a United States Geological Survey expedition. In 1886, he received a Bachelor of Science degree from Kentucky State College (now University) (7). Morgan was particularly interested in the evolution of species. According to the prevailing theory, Darwin's concept of natural selection, within a population there is a certain breadth of variation for each trait. Due to the inheritance of traits within a population, the influence of the environment ensures such a distribution of traits over a number of generations that promotes the survival of individual representatives of the species. At the time Morgan completed his first scientific work, virtually nothing was known about the actual mechanism of inheritance, and the generally accepted method of studying evolution and heredity was to study the morphology and physiology (physical form and function) of representatives of different species to try to draw conclusions about the reasons for their similarities or differences. An important part of such research was the study of embryonic development. In keeping with this practice, Morgan also began studying morphology and physiology when he entered Johns Hopkins University in 1887. Three years later, he received his PhD for research on the embryology of sea spiders (9). In 1891, he became an associate professor of biology at Bryn Myre College, by now very familiar with comparative and descriptive methods. However, like Darwin's theory, these methods did not provide any explanation for the hereditary transmission of traits. Therefore, Morgan turned to experimental techniques, hoping that accurate and verifiable experimental results would eventually answer the desired question. In 1897, while studying the ability of some animals to regenerate lost body parts, a trait apparently closely related to the successful survival of the individual, he published the first of a series of papers on the subject, which he continued to develop throughout his life. In his first special work, “Regeneration” (“Regeneration”, 1901), he emphasized the relationship between the phenomena of regeneration and early embryonic development (2). In 1904, Morgan was appointed professor of experimental zoology at Columbia University. His early works, done within the walls of this institution, were still devoted to experimental embryology.
3. MORGAN FLY
In 1902, biologist W. Sutton proposed that units of heredity (genes) are located inside or on the surface of structures in the cell nucleus called chromosomes. Morgan did not agree with this, believing that chromosomes are products of an early stage of organism development. He liked more the idea expressed by the Dutchman Hugo de Vries, that a new species is formed as a result of mutations. In order to confirm this hypothesis, Thomas Morgan began to look for a convenient object for research. He needed an unpretentious animal with a fast life cycle (1).
Back in 1900–1901, C.W. Woodworth studied Drosophila as experimental material and was the first to suggest that Drosophila could be used in genetic research, in particular, to study inbreeding. Drosophila has only 4 pairs of chromosomes, it begins to reproduce two weeks after its birth and after 12 days brings offspring of 1000 individuals. It is easy to study during a life span of only 3 months. Plus it costs almost nothing. V.E. Castle and F.E. Lutz also worked with Drosophila, who suggested that Morgan work with the fruit fly.
Since 1908, Morgan began observing Drosophila, which was ideal for studying heredity. Morgan's fly-room (6) at Columbia University has become legendary. In many jars and bottles, myriads of flies were hatched from larvae and devoted themselves to science. There were always not enough bottles, and, according to the legend, in the early morning on the way to the laboratory, Morgan and his students stole milk bottles, which Manhattan residents put outside their doors in the evening. By raising flies in glass jars and observing them under a microscope, Morgan discovered the appearance of white-eyed flies, yellow-eyed flies and even pink-eyed flies in addition to the usual red-eyed flies. Over the course of ten years, many different mutants have been discovered in Drosophila.
Morgan crossed flies, observing a huge number of characteristics: eye color, body color, unequal number of bristles, varied shape and size of wings. Analyzing the results of observations, Thomas Morgan came to the conclusion that a number of qualities are transmitted to descendants in the aggregate (8). This made it possible to hypothesize that genes are not scattered throughout the cell, but are linked into certain islands. The fruit fly has only four pairs of chromosomes. Accordingly, Morgan divided the hereditary characteristics of Drosophila into four groups. He came to the conclusion that genes are localized on chromosomes. Each chromosome contains hundreds of genes organized in chains. Thomas Morgan showed that the greater the distance between two genes, the greater the likelihood of a chain break. This meant that distantly located genes could not be inherited together. Conversely, genes that are close to each other are less likely to be separated. Professor Thomas Morgan and his colleagues found that the magnitude of the linear distance between genes can characterize the degree of linkage of genes. Morgan's discoveries made it possible to claim that heredity could be described by precise quantitative methods. Based on his theory, Thomas Morgan mapped the location of genes on Drosophila chromosomes. One of the important discoveries is the “dependence” of certain mutations on sex (Morgan called this phenomenon “linkage” of genes): white eyes in fruit flies were transmitted only to males. This is how sex chromosomes were discovered (1).
After processing a large amount of information, Morgan came to interesting conclusions: genes located on the same chromosome were inherited together much less often than might be expected.
Morgan published his first article about Drosophila in 1910, but his arguments were presented in full force in 1915, when his students - Sturtevant, Bridges and Meller, published the book Mechanisms of Mendelian Inheritance, in which they declared that heredity obeys very specific laws, and it can be described by precise quantitative methods (6). This opened the way to the targeted design of new varieties of plants and animal breeds, to a revolution in medicine and agriculture.
4. FORMATION OF THE CHROMOSOMAL THEORY OF HERITAGE
Human life on Earth is subject to many laws, regulations and theories. A huge number of laws and theories help us uncover some of the secrets of nature, understand what was previously a mystery, and understand the essence of biological laws. One of these most important theories of knowledge of life on Earth is Thomas Morgan’s chromosome theory of heredity.
The theory according to which chromosomes contained in the cell nucleus are carriers of genes and represent the material basis of heredity, i.e. the continuity of the properties of organisms in a number of generations is determined by the continuity of their chromosomes. The theory arose at the beginning of the 20th century. based on cell theory and the use of hybridological analysis to study the hereditary properties of organisms.
The chromosomal theory of heredity is an integral link that “arms” any cytogeneticist. This theory is developing in the direction of deepening knowledge about the universal carriers of hereditary information - deoxyribonucleic acid (DNA) molecules (3). It has been established that a continuous sequence of purine and pyrimidine bases along the DNA chain forms genes, intergenic intervals, and signs of the beginning and end of information reading within a gene; determines the hereditary nature of the synthesis of specific cell proteins and, consequently, the hereditary nature of metabolism.
The chromosomal theory of heredity, explaining the patterns of inheritance of traits in animal and plant organisms, plays an important role in agricultural science and practice. It equips breeders with methods for breeding animal breeds and plant varieties with desired properties. Some provisions of the chromosome theory make it possible to conduct agricultural production more rationally. The study of human hereditary diseases is based on knowledge of the patterns of chromosomal rearrangements, therefore improving knowledge on such an important theory is most relevant at the present stage of the development of life on Earth.
In 1902, W. Setton in the USA, who drew attention to the parallelism in the behavior of chromosomes and Mendelian so-called. “hereditary factors”, and T. Boveri in Germany put forward the chromosomal hypothesis of heredity, according to which Mendelian hereditary factors (later called genes) are localized in chromosomes (4). The first confirmation of this hypothesis was obtained when studying the genetic mechanism of sex determination in animals, when it was found that this mechanism is based on the distribution of sex chromosomes among offspring. Further justification of the chemical technology. belongs to the American geneticist T. H. Morgan, who noticed that the transmission of some genes (for example, the gene that causes white-eyedness in Drosophila females when crossed with red-eyed males) is associated with the transmission of the sex X chromosome, i.e., that traits linked to gender (several dozen such signs are known in humans, including some hereditary defects - color blindness, hemophilia, etc.).
Conclusion
Thomas Hunt Morgan
Thomas Hunt Morgan is a famous biologist and geneticist, winner of the Nobel Prize in Physiology or Medicine for 1933.
Thomas Hunt Morgan was born in Kentucky on September 25, 1866, into a very distinguished, by American standards, family of a diplomat. Morgan was the great-grandson of composer Francis Scott
Key, author of the US anthem.
In 1886, Thomas Morgan graduated from Kentucky State College and received a bachelor's degree.
In 1887, Morgan entered Johns Hopkins University, and in 1890 he received a doctorate for studying the embryos of sea spiders and in the same year he received an Adam Bruce Fellowship, which allowed him to travel to Europe to the Marine Zoological Laboratory. There he met Hans Drich and Kurt Herbst. It was under Driech's influence that Morgan began to become interested in experimental embryology.
In 1888–1889 he was engaged in scientific research at the American Fisheries Committee.
In 1891, Thomas Morgan began work as an associate professor of biology at Bryn Myhra Women's College.
In 1901, Morgan's first fundamental work, Regeneration, was published, devoted to the ability of some species to restore lost body parts.
From 1904 to 1928 he served as professor of experimental zoology at Columbia University (New York), and from 1928 to 1945 - professor of biology and laboratory director at the California Institute of Technology (Pasadena). In the last years of his life, he acquired a small laboratory in Corona del Mar (California).
In 1904 Morgan married Lillian Vaughan Sampson, a student of his from Bryn Mawr.
When the results of August Weismann became known, who found out that hereditary qualities are transmitted using chromosomes, scientists remembered another scientist - Mendel, who had earlier shown that heredity is transmitted by genes.
At first, Thomas Morgan was skeptical of theories that claimed that chromosomes were carriers of heredity. Likewise, Morgan did not accept Darwin's hypothesis of the accumulation of gradual changes.
In 1902, biologist W. Sutton proposed that units of heredity (genes) are located inside or on the surface of structures in the cell nucleus called chromosomes. Morgan did not agree with this, believing that chromosomes are products of an early stage of organism development. He liked more the idea expressed by the Dutchman Hugo de Vries, that a new species is formed as a result of mutations. In order to confirm this hypothesis, Thomas Morgan began to look for a convenient object for research. He needed an unpretentious animal with a fast life cycle.
Back in 1900–1901, C.W. Woodworth studied Drosophila as experimental material and was the first to suggest that Drosophila could be used in genetic research, in particular, to study inbreeding. Drosophila has only 4 pairs of chromosomes, it begins to reproduce two weeks after its birth and after 12 days brings offspring of 1000 individuals. It is easy to study during a life span of only 3 months. Plus it costs almost nothing. V.E. Castle and F.E. Lutz also worked with Drosophila, who suggested that Morgan work with the fruit fly.
Since 1908, Morgan began observing Drosophila, which was ideal for studying heredity.
Morgan's fly-room at Columbia University has become legendary. In many jars and bottles, myriads of flies were hatched from larvae and devoted themselves to science. There were always not enough bottles, and, according to the legend, in the early morning on the way to the laboratory, Morgan and his students stole milk bottles, which Manhattan residents put outside their doors in the evening.
By raising flies in glass jars and observing them under a microscope, Morgan discovered the appearance of white-eyed flies, yellow-eyed flies and even pink-eyed flies in addition to the usual red-eyed flies. Over the course of ten years, many different mutants have been discovered in Drosophila.
Morgan crossed flies, observing a huge number of characteristics: eye color, body color, unequal number of bristles, varied shape and size of wings.
Analyzing the results of observations, Thomas Morgan came to the conclusion that a number of qualities are transmitted to descendants in the aggregate. This made it possible to hypothesize that genes are not scattered throughout the cell, but are linked into certain islands.
The fruit fly has only four pairs of chromosomes. Accordingly, Morgan divided the hereditary characteristics of Drosophila into four groups. He came to the conclusion that genes are localized on chromosomes. Each chromosome contains hundreds of genes organized in chains.
Thomas Morgan showed that the greater the distance between two genes, the greater the likelihood of a chain break. This meant that distantly located genes could not be inherited together. Conversely, genes that are close to each other are less likely to be separated. Professor Thomas Morgan and his colleagues found that the magnitude of the linear distance between genes can characterize the degree of linkage of genes. Morgan's discoveries made it possible to claim that heredity could be described by precise quantitative methods. Based on his theory, Thomas Morgan compiled a map of the location of genes in Drosophila chromosomes.
One of the important discoveries is the “dependence” of certain mutations on sex (Morgan called this phenomenon “linkage” of genes): white eyes in fruit flies were transmitted only to males. This is how sex chromosomes were discovered.
After processing a large amount of information, Morgan came to interesting conclusions: genes located on the same chromosome were inherited together much less often than might be expected.
Morgan published his first article about Drosophila in 1910, but his arguments were presented in full force in 1915, when his students - Sturtevant, Bridges and Meller, published the book Mechanisms of Mendelian Inheritance, in which they declared that heredity obeys very specific laws, and it can be described by precise quantitative methods. This opened the way to the targeted design of new varieties of plants and animal breeds, to a revolution in medicine and agriculture.
Morgan was already approaching fifty and professional recognition was not long in coming. In 1919 he was elected a Foreign Member of the Royal Society of London, and in 1924 he was awarded the Darwin Medal. Morgan became a member of the academies of sciences of different countries (and also, in December 1923, a member of the Academy of Sciences of the USSR). In the late 20s, he headed the US National Academy of Sciences. In 1933, Thomas Morgan was awarded the Nobel Prize in Physiology or Medicine for his discoveries related to the role of chromosomes in heredity.
Morgan died in 1945 in Pasadena.
(1866-1945) American biologist, one of the founders of genetics
Thomas Morgan was born in 1866 in Lexington, Kentucky. At the age of twenty, he graduated from the university of his native state, and 5 years later from Johns Hopkins University in Baltimore. He immediately became a professor at Bryn Mawr College, from 1904 to 1928 he worked as a professor at Columbia University, and from 1928 until the end of his life he headed a laboratory at the California Institute of Technology.
Although the first step towards solving the problem of heredity was made by Mendel when he discovered mathematically correct laws for the transmission of individual properties of an organism to offspring, the development of the science of heredity is still associated with the name of Morgan, because it was he who experimentally substantiated the chromosomal theory of heredity.
Morgan and his collaborators, beginning in 1910, provided irrefutable evidence over about 15 years that genes are linearly arranged on chromosomes; established the facts of gene linkage, that is, their joint inheritance in the case of localization on the same chromosome; discovered the principle of independent divergence of each pair of chromosomes into daughter cells, including germ cells.
Luck accompanied the scientist in his research, largely because he was able to find a living creature for his experiments that was capable of quickly multiplying in a limited space and did not require large maintenance costs. These conditions were fully met by the well-known and widespread fertile fly Drosophila. In order to find out what characteristics of the parents were inherited by the descendants, they were euthanized. Now nothing prevented me from seeing under a magnifying glass what color the flies’ eyes, back, and what shape their wings or abdomen were. When the flies woke up, new generations were obtained from them and the inheritance of traits was monitored further. By comparing the number of traits that are inherited together, Morgan discovered that each Drosophila chromosome contains a group of genes linked to each other. Thus, it was established that genes are indeed located on chromosomes. :
Morgan's merits are not limited to this alone. The scientist discovered numerous deviations from the rule “one chromosome - one group of jointly inherited traits.” Often, traits that were known to be determined by genes belonging to one group turned out in subsequent generations in a new, unusual “company” of other traits. To explain this “disorder,” Morgan made a completely innovative conclusion for that time: the chromosomes of one pair are capable of exchanging parts with each other. Observations of the behavior of Drosophila chromosomes under a microscope confirmed: at a certain stage of meiosis, two chromosomes come closer together, cross over and exchange fragments. In science, this phenomenon is called chromosome crossing, or crossing over.
Morgan and his collaborators imagined chromosomes as necklaces on which beads - genes - were arranged in an orderly manner. This seemingly primitive scheme, especially from the height of our current knowledge, turned out to be very productive. The relative distance between genes on a chromosome began to be determined by simply counting the frequency of “crossover flies.” This is the name given to fly offspring with characteristics the appearance of which can only be explained by the exchange of corresponding sections between the chromosomes of one pair. These calculations formed the basis for the construction of the first genetic maps of the relative location of individual genes on the chromosome.
By the early 20s, American scientists had discovered and localized hundreds of Drosophila genes on chromosomes. Nowadays, about 7000 genes are known in this fly, distributed over four chromosomes. The principles discovered by Morgan formed the basis for the compilation of genetic maps in all animal organisms.
For his work on the study of heredity, Thomas Morgan was awarded the Nobel Prize in 1933. For a number of years he was president of the US National Academy of Sciences, and in 1932 he became an honorary member of the USSR Academy of Sciences.
Born into a wealthy diplomatic family. As a child, I became interested in natural science and had an interest in the exact sciences. In 1886 he graduated from State College (now the University of Kentucky), receiving a bachelor's degree. In 1890 he received a Doctor of Philosophy degree from Johns Hopkins University for research on the embryology of sea spiders. In 1891-1904 he was a professor at Bryn Mawr College (Pennsylvania). In 1904-1928 he was a professor at Columbia University (New York), from 1928 - at the California Institute of Technology.
Morgan's first scientific works concerned experimental zoology and embryology. He later began a systematic study of heredity, which allowed him to expand Mendel's laws. Based on these laws and on the basis of his own experiments, Morgan developed the chromosomal theory of heredity, the main provisions of which opened the way for his followers to new research and led to the flowering of cytogenetics, i.e. cellular and biochemical genetics. For his work on the study of heredity, Morgan was awarded the Nobel Prize in 1933.
The following works of Morgan are considered the most important: “Regeneration” (1901), “Experimental Zoology”, “Heredity and Sex” (1913), “Criticism of the Theory of Evolution”, “Physical Basis of Heredity” (1932), “Genetics of the Drosophila Fly” (together with Bridges and Sturtevant), "The Theory of the Gene" (1932).
Morgan was a follower of A. Weissman in the matter of cell research, who came to the conclusion about the continuity of the germplasm, which has signs of heredity and is distinguished by a precisely expressed chemical structure. But he was unable to answer the question of what exactly determines the similarity between offspring and parents. Weisman's theory has spread throughout the world.
Long and difficult studies of the phenomenon of heredity and variability of species ended in success only after Morgan's experiments with the Drosophila fly. The scientist developed the theory of genes as carriers of certain hereditary properties; he divided all the studied properties of the Drosophila fly into four groups, which are inherited and associated with the presence of four pairs of chromosomes in the Drosophila fly. Scientists have suggested that combinations of these chromosomes cannot exceed thousands of different genes. Depending on what genes a fly has, it will belong to one species or another. Thousands of experiments carried out with Drosophila allowed Morganists to draw maps that could be used to determine where a particular gene is located on a chromosome, which made it possible to assume that in the chromosomes of all plants and animals each gene is located in a precisely defined position.
Thus, Morgan substantiated the chromosomal theory of heredity; The patterns of gene arrangement on chromosomes he established contributed to the elucidation of the cytological mechanisms of Mendel's laws and the development of the genetic foundations of the theory of natural selection.