THOMAS HUNT MORGAN: BIOGRAPHY, CHROMOSOME THEORY, EXPERIMENTS - ARTE - 2025

Thomas Hunt Morgan (1866-1945) was an American scientist specializing in the study of genes. Born in September 1866, his greatest contribution was to demonstrate the veracity of the chromosomal theory of genes developed by Sutton and Boveri. His work proved that sex chromosomes existed, as well as the so-called "sex-linked inheritance."

In order to confirm this theory, the geneticist conducted several experiments with the fruit fly (Drosophila melanogaster). His main intention was to see if Gregor Mendel's theories were true and if they could be applied to animals.

Thomas Hunt Morgan - Source: Carl A. Gist / Public domain

Morgan, who had had a tough childhood and youth, showed an early interest in science, especially natural history. During his professional career, he participated in several of the hottest scientific debates of the time, from Darwin's theory to the formation of embryos.

Even in retirement, Morgan continued to conduct research on various topics. After his death, the Genetics Society of America established in his honor an annual award to recognize the most important research on the subject: the Thomas Hunt Morgan Medal.

Biography

Thomas Hunt Morgan was born on September 25, 1866 in Lexington, Kentucky (USA). According to some of his biographers, young Thomas had a very tough youth.

Studies

When Thomas was 16 years old, he began studying at the State College of Kentucky, now a state university. His training during this period was focused on science, especially natural history. During vacation periods he worked for the United States Geological Survey.

In 1866, Morgan finished this phase of his studies with a Bachelor of Science degree. That same year, in the summer, she moved to Massachusetts to attend Biology School. It was at this center, which belonged to John Hopkins University, that he began to show interest in zoology.

During the next two years Morgan published several works. His intelligence allowed him to be selected to receive a master of science at his old Kentucky center, State College. He also offered him a teaching position. However, Morgan preferred to remain at John Hopkins.

Young Morgan did his thesis on the embryology of sea spiders. This work, which was published, earned him his doctorate in 1890.

The scientist used the money obtained from the publication of his thesis to make a trip to the Caribbean and Europe. During the same he continued investigating various zoological subjects.

Career

The same year that Morgan obtained his doctorate, he received an offer to work as a professor of morphology at the Bryn Mawr School, a center twinned with John Hopkins. His job was to give lectures five days a week, twice a day. This left him little time to research, an activity he wanted to focus on.

Trip to Europe

That opportunity to investigate came to him in 1894, when he moved to Naples to carry out a series of studies on the embryology of ctenophores, a form of life almost microscopic in size.

In the Italian city he came into contact with German scientists. These explained to him the new theories about the mechanics of development, which supposed an overcoming of those in force in the 19th century.

One of the scientific debates of the time focused on the development of embryos. One of the theories maintained that the hereditary material was divided between the embryonic cells and that these later became specific parts of the organism.

Other experts, however, claimed that development was caused by epigenetic factors. Morgan was in favor of this second hypothesis.

Columbia university

After Morgan returned to Bryn Mawr, in 1895, he began working full time. This situation lasted until 1904, when he received an offer to join Columbia University as a researcher, without having to teach.

Morgan, who the previous year had published Evolution and Adaptation in which he was contrary to some of Darwin's theses on the mechanisms of national selection, accepted the offer.

A few years later, in 1908, Morgan began his experiments with the fruit fly. Using chemistry and radiation, he caused mutations in some specimens. The results confirmed the theory established by Sutton and Boveri.

At the end of his work with the fruit fly, the scientist resumed his studies on embryology. In addition, he also investigated how genes are inherited.

In 1915 he participated in a new scientific debate that was developing: eugenics and the defense of racism from science. Morgan was against these ideas.

Last years

Years later, in 1928, Morgan took over the department of biology at the California Institute of Technology. In this new position he carried out research on genetics, physiology, evolution, embryology or biophysics.

Morgan remained working in that institution until 1942, the year in which he retired. However, he kept his position as professor emeritus and, furthermore, continued to do research in some fields.

Thomas Hunt Morgan passed away from a heart attack on December 4, 1945, when he was 79 years old.

Chromosomal theory of heredity

Although the chromosomal theory of inheritance was not the work of Morgan, it was his studies that confirmed his postulates.

Boveri and Sutton

The authors of the theory were Theodor Boveri and Walter Sutton. The two researchers, working separately, reached the same conclusions in 1902.

However, the theory encountered considerable opposition among the scientific community. Acceptance came in 1915, when Thomas Hunt Morgan conducted experiments that proved Sutton and Boveri right.

The theory

In summary, the chromosomal theory of inheritance states that genes are located in specific locations on the inside of chromosomes. Their behavior during meiosis (one of the forms of reproduction of cells) explains Mendel's laws of inheritance.

The authors of the theory analyzed genes, that is, those DNA fragments that contain hereditary factors. Before these studies, it had already been possible to prove the existence of chromosomes and that they replicated during cell division. However, thanks to Boveri and Sutton, many other details came to light.

Among other things, they discovered that chromosomes go in homologous pairs, one from the mother and the other from the father. Each gamete, therefore, contributes half of the genetic material to the person.

The theory increased understanding of why some aspects are inherited and others are not. Thus, for example, it is known that one chromosome contains the information about the different sex, while another provides the information about the color of the eyes. The independence of each trait means that some are transmitted and others are not.

Morgan Confirmation

As noted, the chromosome theory was not accepted at first. Morgan, with his experiments with the fruit fly, was able to provide the necessary evidence to demonstrate its veracity.

Morgan noted that when meiosis occurred, there were pairs of chromosomes that could exchange some equivalent fragments with each other. Thus, fragments of DNA were exchanged and, therefore, the so-called genetic recombination took place.

Experiments performed

EB Wilson, director of the department of zoology at Columbia University, convinced his friend Thomas Hunt Morgan in 1904 to take up a newly created position and to take up experimental zoology.

Wilson's argument was that it was necessary to understand how genetic inheritance occurs in order to understand the development of a complete individual.

Morgan accepted the offer and began experimenting with rats and mice. However, the characteristics of these animals were not adequate. Instead, the scientist opted for Drosophlia melanogaster, the fruit fly.

The advantages of this insect were multiple: its small size, which allowed to keep thousands in the laboratory; its fertility throughout the year; and its enormous reproductive capacity. In addition, it was very easy to distinguish between males and females and their embryonic development occurs outside. The latter facilitated the study of mutations.

The last reason for choosing the fruit fly was its simplicity - it only has four pairs of chromosomes.

Morgan began his experiment in 1907. Initially, he intended to maintain the fly colony for only several generations, until a mutation occurred. However, the following two years did not produce results.

White eyes

In 1909, after two years of work, the efforts of Morgan and his team paid off. The scientist observed that one of the flies in the laboratory had a strange mutation that he called "white eyes" because his eyes had that color instead of the reddish color typical of the species.

The insect was male and Morgan used it to inseminate several females. Its purpose was to check if the mutation passed to the new generations. However, all the offspring kept their eyes red.

This made Morgan think that something strange had happened. Her next step was to cross a couple of the daughter flies to see what would happen. On this occasion, to the surprise of the scientist, several of the resulting specimens had the white eyes of their "grandfather". Given this result, Morgan went to work trying to explain what happened.

Sex-linked inheritance

The results of the investigations led Morgan to propose the hypothesis that heredity was linked to sex. Thus, the scientist affirmed that there were characters linked to the mother's X chromosome.

Later, Morgan found other characteristics that were inherited in the same way, confirming his theory. It was then that he began to use the word gene or genes to describe the factors that passed from generation to generation along the X chromosome.

For Morgan, all those genes were part of the chromosomes. These, together, shaped the individual and species genetic inheritance.

Other contributions

Thomas H. Morgan continued to work with chromosomes to try to understand even better how genetic inheritance occurred. To do this, he drew linear chromosome maps, with each gene in a specific position. This ended up showing that the genes responsible for the transmission of characteristics lined up within each chromosome.

This research was presented in a book that became a reference for modern genetics: The mechanism of Mendelian inheritance.

Gene theory

In 1926, Morgan presented his theory of genes. This claimed that genes were linked in different chaining groups. Alleles (pairs of genes related to the same genetic characteristic) were always exchanged or crossed within the same group. This discovery earned him the 1933 Nobel Prize in Physiology and Medicine.

References

1. EcuRed. Thomas Hunt Morgan. Obtained from ecured.cu
2. Khan Academy. The chromosomal basis of inheritance. Retrieved from es.khanacademy.org
3. Whose Reyes, Arturo. Thomas Morgan. Obtained from innovations.pe
4. DNA Learning Center, Cold Spring Harbor Laboratory. Thomas Hunt Morgan (1866-1945). Retrieved from dnaftb.org
5. The Nobel Prize. Thomas H. Morgan. Retrieved from nobelprize.org
6. Nature Education. Thomas Hunt Morgan: The Fruit Fly Scientist. Retrieved from nature.com
7. Allen, Garland Edwards. Thomas Hunt Morgan. Retrieved from britannica.com