Biography. Scientific contributions of Thomas Hunt Morgan T Morgan biography
morgan scientist chromosome heredity
Thomas Morgan and his students (G. J. Meller, A. G. Sturtevant, etc.) 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 and the development of the genetic foundations of the theory of natural selection.
Surprisingly, many scientific discoveries are based not only on strong knowledge, talent and perseverance. Often, success simply requires intuition and luck. For example, the extraordinary success of Mendel's experiments is largely due to the fact that the scientist intuitively chose a wonderful object for experiments - peas. The subsequent failure, which forced Mendel to abandon further research, was also the result of the choice of experimental subjects - this time unsuccessful. Morgan for his research chose not just a successful, but an ideal object, which over time became the most famous genetic model - the Drosophila fruit fly (Fig. 22).
Drosophila has become an ideal object for genetic research due to its properties: the fly has only 4 pairs of chromosomes, its life cycle is 10-20 days, during which one female gives birth to about 400 offspring.
Fruit flies are easy to study throughout their lives. In addition, the cells of the salivary glands of Drosophila larvae contain giant chromosomes, which are very convenient for research since they do not require microscopes with very high magnification.
Since 1908, Morgan began his research. At first, he bought fruit flies from grocery and fruit stores.
He caught them with a net, having received permission from the store owners, who made fun of the eccentric flycatcher. The thirty-five-meter experimental room, the so-called “fly room” at Columbia University, where Morgan conducted his research, quickly became the talk of the town. The entire room was filled with bottles, jars, bowls and flasks, in which thousands of flies were flying, voracious larvae were swarming, all the glass of these vessels was hung with fruit fly pupae. There were not enough bottles, and there were rumors that early in the morning, on the way to the laboratory, Morgan and his students stole milk bottles, which Manhattan residents put outside their doors in the evening!
Morgan studied the flies he raised. It turned out that they are quite different in appearance: in addition to the usual red-eyed flies, there are white-eyed, yellow-eyed and even pink-eyed flies. There are flies with long and short wings and flies with curved, wrinkled wings that are unable to fly. Drosophila differ in the shape and color of their abdomen, legs, antennae, and even the bristles covering their body.
Morgan crossed fruit flies, monitoring the inheritance of a huge number of all these traits. Analyzing the results of observations, he came to the conclusion that some characteristics are passed on to descendants together. Based on this, Morgan suggested that the genes that determine these “linked” traits are not scattered throughout the cell, but are linked in special “islands.” It turned out that all the hereditary characteristics of the fly are divided into four “linked” groups. It was already known that Drosophila has four pairs of chromosomes. From this Morgan concluded that genes are localized on chromosomes, with each chromosome containing a chain of hundreds of genes. The scientist found that the greater the distance between two genes on a chromosome, the higher the probability of a chain break - genes located close to each other are extremely rarely separated. Based on these observations, Morgan mapped the location of genes on Drosophila chromosomes. This happened a year after the term gene was approved in science.
In addition, Morgan found that some traits are transmitted only to males or only to females. He concluded that the genes responsible for these traits are localized on the chromosomes that determine sex. Thus, the existence of sex chromosomes was discovered to them.
Morgan's study of fruit flies resulted in the chromosomal theory of heredity. We will study it a little later. The main postulate of this theory is this: the material basis of heredity is the chromosomes in which genes are localized.
In 1933, Thomas Morgan was awarded the Nobel Prize in Physiology or Medicine “for his discoveries concerning the role of chromosomes in heredity.” He is the only one of the founders of genetics who received such an honor.
Thus, at the very beginning of the history of genetics, two fundamental milestones can be identified that determined the essence of this science. The first is the stage of hybridological research, which began with Mendel’s experiments, which proved the existence of certain discrete hereditary factors that are transmitted from parents to descendants, obeying certain mathematical laws. The second is cytological studies, based primarily on Morgan's experiments, which proved that chromosomes are carriers of hereditary factors.
Rice. 1. Drosophila is the most popular object of genetic research: a - male; b -- female
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"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 the 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 embryology 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 was reluctant 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: “The laws of Mendel and Morgan 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 - American biologist, 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, president of the US National Academy of Sciences (1927-31), chairman of the Sixth International Congress on Genetics in Ithaca, New York ( 1932). Winner of the 1933 Nobel Prize in Physiology or Medicine “for his discoveries concerning the role of chromosomes in heredity.”
Thomas 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. He was the eldest son and first of three children of diplomat Charlton Hunt Morgan and Helen (Key-Howard) Morgan (her grandfather was the American composer Francis Scott Key - author of the US national anthem).
Since childhood, Thomas showed interest in natural history and the exact sciences, and collected a collection of different species of birds. In 1886, Thomas Morgan graduated from Kentucky State College with a bachelor's degree, particularly interested in the evolution of species at the time when there was little scientific knowledge about the actual mechanism of heredity. The summer immediately after graduation, he went to the Ennisquam naval station on the Atlantic coast, north of Boston. Over time, he worked on an expedition of the US Geological Survey, conducting geological and biological searches in the mountains of Kentucky.
IN 1887 Morgan entered Johns Hopkins University, where he studied animal morphology and physiology. And in 1890 (Three years later) he received a Doctor of Philosophy degree for research on the embryology of sea spiders and in the same year he received an Adam Bruce Fellowship, which allowed him to go 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. 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. 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 In the same year, Morgan moved to Woods Hole, and in the summer of the same year he began working at the State Fisheries Station.
IN 1889 engaged in scientific research at the American Fisheries Committee.
IN 1890 received his doctorate from Johns Hopkins University and in the same year 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 one of his early works, Morgan criticizes the Mendelian theory of heredity. He believed that chromosomes are not carriers of heredity, but are products of early stages of development. He also did not support Darwin’s idea of “gradual change,” preferring the version of the Dutch botanist Hugo de Vries that the emergence of a new species is the result of mutations. At that time, almost nothing was known about the mechanism of inheritance, and the method of studying the process of evolution and heredity was to compare the morphology and physiology of representatives of different species. Based on the data obtained, scientists tried to draw conclusions about the reasons for the similarities or differences between existing species. Morgan was no exception; his first works on the study of heredity were carried out in accordance with generally accepted methods.
TO 1891 He fully mastered the comparative and descriptive methods of research, but they did not provide answers to the questions that interested him, and he turned to experiments, hoping to obtain a specific result. In 1891, Thomas Morgan began work as an associate professor of biology at Bryn Myhra Ladies' College.
IN 1897 year he was elected one of the trustees of the naval station, and he 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.
IN 1900 The focus of attention of geneticists around the world was Mendel's work on the inheritance of traits in peas. In these works, Mendel argued that traits are inherited according to strict mathematical laws.
IN 1901 In 2010, Morgan’s first fundamental work, “Regeneration,” was published, devoted to the relationship between the phenomena of regeneration and the early embryonic development of the organism. 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.
IN 1902 biologist W. Sutton suggested that units of heredity (genes) are located inside or on the surface of structures of 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.
Wilson in 1904 year convinced Thomas Morgan to take the professorship of experimental zoology at Columbia University. For twenty-four years they worked in very close communication. Like most biologists-zoologists of the 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 embryology with inferences extending into the realm of phylogeny. His own scientific gift inclines him to study the problems of barely emerging genetics; the results of G. Mendel’s research on the hereditary traits of beans aroused particular interest. 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.
In the same year, Thomas Morgan married Lilian Vaughan Sampson, a cytologist by profession, his student from Bryn Mawr. They had four children.
WITH 1904 to 1928 served as professor of experimental zoology at Columbia University (New York). 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.
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 was reluctant 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 Morgan could rather be considered an anti-Mendelian.
1908 d. Having started his experiments, Morgan first caught fruit flies in grocery and fruit shops, fortunately the shopkeepers, who were annoyed by the flies, willingly allowed the eccentric to catch them. Thomas Morgan experiments with the fruit fly Drosophila melanogaster, which has only four chromosomes. Numerous experiments have made it possible to establish a direct relationship between chromosomes and heredity.
IN 1909 Morgan began working with the fruit fly Drosophila. Very soon (in 1909) the first mutations appeared. Subsequent study of this phenomenon ultimately allowed the scientist to establish the exact location of the genes and the principle of their operation. One of the most important discoveries can be considered the “dependence” of certain mutations on gender (Morgan called this phenomenon “linkage” of genes): white eyes in fruit flies were transmitted only to males. 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. Consequently, it is possible for chromosomes to split and exchange genetic material between chromosomes and genes. The farther apart genes are located on a chromosome, the higher the likelihood of them being broken. Based on this, Morgan and his colleagues compiled “maps” of Drosophila chromosomes. His guess about the “linear” arrangement of genes on a chromosome, and that the “linkage” of genes depends on the distance of one gene from another, is one of the revolutionary discoveries in genetics.
Morgan's fly-room at Columbia University has become legendary. 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. 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. 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.
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.
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. 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. 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.
WITH 1911 years, Morgan and his associates began to publish a series of works in which experimentally, on the basis of numerous experiments with fruit flies, it was proved that genes are material particles that determine hereditary variability, and that their carriers are the chromosomes of the cell nucleus. Then the chromosomal the theory of heredity that confirmed and reinforced 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 unless he forged several things out of hot water at the same time.”
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.
At first 1912 A.H. Sturtevant and K.B. Bridges, then still students at Columbia University, joined the group of researchers. The team of scientists came to the conclusion that chromosomes in a pair can split and recombine, thereby facilitating the exchange of genes, and the greater the distance between two genes on the same chromosome, the more likely it is that the process will fail. 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 on Drosophila in 1910 -year, but his arguments were presented in full force in 1915 -m, when his students - Sturtevant, Bridges and Meller, published the book Mechanisms of Mendelian Inheritance, in which they announced that heredity obeys well-defined laws and 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 1916 Morgan presented a series of lectures at Princeton University, later published as a critic of the theory of evolution, the Mendelian theory of heredity, and Darwin's theory of natural selection. He formulated a revised version of Darwin's theory of natural selection, which became known as the modern evolutionary synthesis.
IN 1919 he was elected a Foreign Member of the Royal Society of London and was awarded the Darwin Medal in 1924; 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 same year, his book was published: The Mechanism of Mendelian Inheritance. In the late 20s, he headed the US National Academy of Sciences.
1924 year. Morgan was awarded the Darwin Medal, the highest award of the Royal Society of Great Britain. Awarded for outstanding achievements in biology, in those areas in which Charles Darwin worked.
IN 1928 Morgan moved to the California Institute of Technology in order to organize a new biological 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 . 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 1932 his book “Roles of Mutation, Inbreeding, Crossbreeding and Selection in Evolution” was published.
IN 1933 Thomas Morgan was awarded the Nobel Prize in Physiology or Medicine "for his discoveries concerning the role of chromosomes in the heredity of an organism" for discoveries related to the role of chromosomes in heredity. After receiving the Nobel Prize, Thomas Hunt Morgan continued his administrative work at Caltech, combining it with the study of biological regeneration in pigeons, salamanders and rare species of mice. Morgan was a very generous person in life and often financed the education of especially gifted students.
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 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.”
1941 Mr. Thomas Morgan received the title of Professor Emeritus of Biology at Caltech.
Morgan loved to tease, loved to play tricks. 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. Morgan's two most swear words were "metaphysical" and "mystical." The word “metaphysical” meant for him something connected with philosophical dogma, a certain explanation that was not verifiable by experience.
In the last years of his life, he acquired a small laboratory in Corona del Mar (California).
1. The founder of the chromosome theory, Thomas Gent Morgan, American geneticist, Nobel laureate. Morgan and his students found that:
– each gene has a specific locus(place);
– genes on a chromosome are located in a certain sequence;
– the most closely located genes on one chromosome are linked, therefore they are inherited predominantly together;
– groups of genes located on the same chromosome form linkage groups;
– the number of clutch groups is equal haploid set of chromosomes homogametic individuals and n+1 heterogametic individuals;
– between homologous chromosomes there can be an exchange of sections ( crossing over); as a result of crossing over, gametes arise whose chromosomes contain new combinations of genes;
– the frequency (in%) of crossing over between non-allelic genes is proportional to the distance between them;
– set of chromosomes in cells of a given type ( karyotype) is a characteristic feature of the species;
– the frequency of crossing over between homologous chromosomes depends on the distance between genes localized on the same chromosome. The greater this distance, the higher the crossing over frequency. The unit of distance between genes is taken to be 1 morganid (1% crossing over) or the percentage of occurrence of crossing over individuals. If this value is 10 morganids, it can be stated that the frequency of chromosome crossings at the locations of these genes is 10% and that new genetic combinations will be identified in 10% of the offspring. To clarify the nature of the location of genes on chromosomes and determine the frequency of crossing over between them, genetic maps are constructed. The map reflects the order of genes on a chromosome and the distance between genes on the same chromosome. These conclusions of Morgan and his colleagues were called the chromosomal theory of heredity. The most important consequences of this theory are modern ideas about the gene as a functional unit of heredity, its divisibility and ability to interact with other genes.
2. Chromosome sets of different sexes differ in the structure of sex chromosomes. The male Y chromosome does not contain many of the alleles found on the X chromosome. Traits determined by the genes of the sex chromosomes are called sex-linked. The pattern of inheritance depends on the distribution of chromosomes in meiosis. In heterogametic sexes, traits that are linked to the X chromosome and do not have an allele on the Y chromosome appear even when the gene that determines the development of these traits is recessive. In humans, the Y chromosome is passed from father to sons, and the X chromosome to daughters. Children receive the second chromosome from their mother. It is always the X chromosome. If the mother carries a pathological recessive gene on one of the X chromosomes (for example, the gene for color blindness or hemophilia), but is not sick herself, then she is a carrier. If this gene is passed on to sons, they may end up with this disease, because the Y chromosome does not have an allele that suppresses the pathological gene. The sex of an organism is determined at the moment of fertilization and depends on the chromosome complement of the resulting zygote. In birds, females are heterogametic, and homogametic– males.
3. An example of sex-linked inheritance. It is known that in humans there are several traits linked to the X chromosome. One such sign is the absence of sweat glands. This is a recessive trait; if the X chromosome carrying the gene that determines it gets to a boy, then this trait will certainly manifest itself in him. If you read Patrick Suskind's famous novel "Perfume", then you remember that it was about a baby who had no smell. Consider an example of sex-linked inheritance. The mother has sweat glands, but she is a carrier of a recessive trait - Chr X, the father is healthy - XY. Mother's gametes - Xp, X. Father's gametes - X, U.
From this marriage, children with the following genotypes and phenotypes can be born:
Nonallelic genes can also interact with each other. An example of such interaction could be the appearance of new growths when crossing two outwardly identical forms. For example, the inheritance of comb shape in chickens is determined by two genes - R and P: R - rose-shaped comb, P - pisiform comb.
F1 RrPp – appearance of a nut-shaped ridge in the presence of two dominant genes; with the ggrr genotype, a leaf-shaped ridge appears.
Questions for self-control on the topic:
1. How many pairs of chromosomes are responsible for the inheritance of sex in dogs if their diploid set is 78?
1) one 2) two 3) thirty-six 4) eighteen
2. Patterns of linked inheritance apply to genes located in:
1) different non-homologous chromosomes 2) homologous chromosomes
3) on one chromosome 4) non-homologous chromosomes
3. A colorblind man married a woman with normal vision, a carrier of the colorblind gene. What genotype cannot they have a child with?
1) ХdХ 2) XX 3) ХdХd 4) ХУ
4. What is the number of gene linkage groups if it is known that the diploid set of chromosomes of an organism is 36?
1) 72 2) 36 3) 18 4) 9
5. The frequency of crossing over between genes K and C is 12%, between genes B and C – 18%, between genes K and B – 24%. What is the probable order of genes on a chromosome if they are known to be linked.
1) K-S-V 2) K-V-S 3) S-V-K 4) V-K-S
6. What will be the phenotypic cleavage in the offspring obtained from crossing black (A) shaggy (B) guinea pigs heterozygous for two traits linked on one chromosome?
1) 1: 1 2) 2: 1 3) 3: 1 4) 9: 3: 3: 1
7. From crossing two gray rats heterozygous for two color traits, 16 individuals were obtained. What will the ratio of offspring be if it is known that gene C is the main color gene and in its presence gray, white and black individuals appear, and the second gene A affects the distribution of pigment. Gray individuals appear in his presence.
1) 9 grey, 4 black, 3 white 2) 7 black, 7 black, 2 white
3) 3 black, 8 white, 5 gray 4) 9 gray, 3 black, 4 white
8. A married couple had a hemophiliac son. He grew up and decided to marry a healthy woman who does not carry the hemophilia gene. What are the possible phenotypes of the future children of this couple if the gene is linked to the X chromosome?
1) all girls are healthy and not carriers, and boys are hemophiliacs 2) all boys are healthy, and girls are hemophiliacs 3) half of the girls are sick, boys are healthy
4) all girls are carriers, boys are healthy
9. Make a forecast for the appearance of a colorblind grandson for a colorblind man and a healthy woman who does not carry the colorblind gene, provided that all his sons marry healthy women who do not carry the colorblind gene, and his daughters marry healthy men. Support your answer by recording the crossing pattern.
The biography of the great American geneticist Thomas Morgan reflects the main milestones of his life and research achievements that made it possible to successfully develop molecular biology over many years.
American scientist Thomas Morgan is rightfully considered one of the greatest biologists who made great discoveries for all mankind. He achieved outstanding success in the study of chromosomes and genes, which put molecular biology on a fundamentally new level and made it possible to resort to experimental methods of research in genetics.
Thanks to him and Gregor Mendel, successful work was subsequently carried out on deciphering the genome, in the field of transgenic selection and genetic engineering.
Be born at the right time
In Morgan's biography you will not find evidence of persecution for his beliefs, non-sharing of views by colleagues, or oblivion at a certain stage of his life's journey. It was a long and happy life, always close to loved ones, a successful career as a teacher and researcher, who is still considered a genius of fundamental genetics. Representatives of this science even today more often receive the Nobel Prize than researchers in other fields. At the beginning of the 20th century, thanks to the work of Morgan and colleagues, important genetic data were accumulated, results of research into the mechanism of cell division (meiosis and mitosis) appeared, and conclusions were drawn about the role of chromosomes and the cell nucleus in the inheritance of traits.
Thus, the chromosome theory made it possible to understand the cause of the appearance of hereditary diseases in humans and made it possible to experimentally change hereditary information, becoming the starting point for modern genetic research. Although he was not a discoverer, he managed to formulate the postulates of a theory that changed the whole world. In fact, after Morgan’s developments, topics such as life extension, growing new organs, human transformations remain only matters of time in modern reality.
Aristocratic origin
Thomas Morgan, born in the United States on September 25, 1866, is the nephew of Gent Morgan, the famous military leader of the Confederate Army, and the son of Hunt Morgan, the American consul in Sicily and a successful diplomat. The scientist's maternal grandfather was the author of the American national anthem. Since childhood, the boy was drawn to sciences such as geology and biology, and already at the age of 10 he was interested in searching for unusual stones and studying bird eggs and feathers. Having matured a little, Thomas helped participants in expeditions of the US Geological Survey in his native places. And at the age of 20, he receives a bachelor's degree after graduating from college.
Student time
At the university, the young man devotes a lot of time to the physiology and morphology of animals. The first scientific work concerned the physiology and structure of sea spiders. Then it was the turn of embryology. The young scientist becomes a master's degree, defends his dissertation and heads the biological department of Bryn Mayr College. This was followed by an internship at the Naples Zoological Laboratory in 1894 and the beginning of research into hereditary traits.
At that time, the debate between preformationists, who were confident in the presence of structures in gametes that determine the development of the organism, and epigenists, who argued that the formation of the organism is influenced by external factors, was very relevant. In this case, Morgan stands in the middle between positions. In 1895, Thomas became a professor and soon published two books: Development of the Frog's Egg and Regeneration. The priority areas of his activity still remain evolution and heredity. The scientist married in 1904 to Lilian Vaughan Sampson, his student, who not only gave birth to four children, but also became a reliable research assistant.
Columbia University
Working at the university since 1903 in the department of experimental zoology, in 24 years Thomas Morgan managed to make the most significant discoveries in history in the field of inheritance and evolution. Researchers of the time were looking for confirmation of Mendel's theory regarding natural selection, and Morgan, at the age of 43, personally verified the validity of his colleague's research. As a result of his successful work, he acquired the title of “Lord of the Flies” for many years. As the object of his experiments, he chooses fruit flies, which become the “sacred cow” of geneticists for the entire coming century.
The most important thing is that these flies have only 4 chromosomes, which can be easily studied throughout the entire 3 months of Drosophila life. Scientist Thomas Morgan’s successful experiments were helped by his talented students, who took an active part in organizing laboratory No. 213, the legendary “fly room” within the walls of Columbia University.
Innovation in teaching
That same world-famous Colombian laboratory became a place for study visits for many famous scientists. Thanks to this small room with an area of only 24 square meters, the organization of the educational process itself was changed. Morgan based his work on the principles of democracy, lack of subordination, free exchange of opinions, brainstorming, and complete transparency. His methodology became the basis for teachers of American universities, and then European ones.
For two long years, Morgan and his colleagues have been struggling almost to no avail to solve the issues of inheritance of mutations. However, then a real miracle happens - flies with altered characteristics are born, which later made it possible to formulate the theory of inheritance. Crossing individuals, counting thousands of descendants, thousands of bottles of fruit flies - all this became the price of the scientist’s success. Evidence was obtained of sex-linked inheritance and storage of trait data on a specific chromosomal site. The results were compiled into a paper entitled “Sex-Linked Inheritance.”
Chromosome theory
The successful result of all the activities of Thomas Morgan is the substantiation of the theory of inheritance. Its basis is that the material basis of heredity is chromosomes, where genes are arranged in a linear order. Morgan discovered linked genes that are inherited together, as well as traits that are inherited according to sex.
Recognition of achievements
Over the course of several years, Thomas Morgan became a member of many academies around the world, including the USSR Academy of Sciences in 1923. And 10 years later, the scientist was awarded the high title of Nobel Prize laureate for his discoveries in the field of the influence of chromosomes on heredity. Morgan shared the prize with his colleagues Startevant and Bridges. The collection of the great scientist includes the Darwin Medal donated in 1924, the Copley Medal in 1939, the Faculty of Biology at Kentucky State is named in his honor, as well as the Genetics Society of America Award, which is held annually. In addition, in genetics there is the concept of a morganide - a unit of gene linkage. Since 1928, he led the Kirchhoff Laboratory at the California Institute of Technology for many years. The cause of the scientist's death in 1945 was stomach bleeding.
As a conclusion
Of course, Thomas Morgan made invaluable contributions to biology, which are comparable to the first flight into space or the discovery of the atomic nucleus in physics. He was a noble and kind man with a good sense of humor, unpretentious in everyday life and always self-confident. He did not pursue fame, did not dream of becoming a legend, but, on the contrary, wanted to rid humanity of myths and prejudices. The geneticist had an excellent understanding of the subject he studied. Despite all his great discoveries, Thomas Morgan was able to remain simply a biologist throughout his life.
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