Concept


Thomas Hunt Morgan and his students at Columbia University ushered in the era of modern genetics when they showed the physical basis of heredity. Where Mendel had bred pea plants, the Columbia group studied inheritance in the common fruit fly. Unlike Mendel, who found readily identifiable traits, they spent months searching for a fly with any unique trait that could be studied. Finally they discovered a single white-eyed male fly, which stood out from its normal, red-eyed peers. A cross between the mutant male and a red-eyed female produced only red-eyed offspring. White-eyed mutants reappeared in the following generation — the classic pattern of a recessive trait. However, the white-eyed trait was seen exclusively in males of the second generation. They concluded that white-eyed is a sex-linked recessive trait. The gene for eye color must be physically located on the X chromosome.

Animation


Hi, I'm Thomas Hunt Morgan. In 1904, I started the "Fly" lab at Columbia University to study genetic variations. Many of the important discoveries of genetics and chromosomal inheritance came out of my lab through research using fruit flies. It all started when we found our first useful fruit fly mutation. Flies normally have red eyes but in January, 1910, we found a male with white eyes. We immediately crossed this male with a "wild type" female with red eyes. All the offspring of the first generation were red-eyed! We next crossed males and females from the first generation to each other. The white-eye trait reappeared in the expected 3:1 Mendelian ratio for a recessive trait. However, only the males had white eyes. This suggested that the white-eye trait is carried on the X chromosome. A Punnett square predicts the same results. I used a small "w" for the recessive white and a large "R" for the dominant red. Drosophila mutants are named according to the phenotype of the mutations. Crossing white-eyed males and red-eyed females from the second generation produced equal numbers of offspring with each eye color. Males have white eyes when they inherit the mutant gene on the X chromosome from their mother. Females only show the trait if they inherit mutant genes on both X chromosomes. I called this phenomenon "sex-limited" inheritance, but it became known as "sex-linked" or "X-linked." Within several years, we found more than 80 different mutations in fruit flies. Here are some of the flies from our fly library. Let's bring them all back so that we can compare. I became convinced that these little animals could show us the physical basis of heredity. So began my conversion from an experimental evolutionist to a geneticist.

Gallery


Early drawing of a male fruit fly.
Family portrait of the Morgans. Thomas Hunt Morgan is standing next to his father on the right (around 1874).
Signed and dated photo of T. H. Morgan.
Morgan in the Fly Room at Columbia, 1917. Note the large number of fly cultures.
Morgan, in the Fly Room at Columbia, 1917. In the lab, Morgan was called "The Boss." This picture was taken by A.H. Sturtevant.
The Fly Room at Columbia University, around 1920. Note the bananas used as fruit fly food. The room no longer exists at Columbia.
Morgan at his desk at Columbia, 1920.
Morgan at work. Note the single ocular microscope; the binocular microsope was not a favored tool of Morgan's.
New York Times article the day T.H. Morgan won the Nobel Prize for Medicine, December 11, 1933. Supposedly, when asked for a pose, Morgan insisted on this more casual picture with children.

Audio/Video


Audio Glossary

Chromosome, Dominant, Gene, Recessive, Sex-linked

Video Interviews

Garland Allen

Garland Allen is a Professor in the Evolutionary and Population Biology Program at Washington University in St. Louis. He authored Thomas Hunt Morgan: The Man & His Science, and several texts, including Matter, Energy and Life and The Study of Biology.

Clip 1 (0:55)
A description of the "Chromosome debate" that took place during Morgan's time.

Clip 2 (0:45)
Summary of the Chromosome "theory" pre-Morgan.

Clip 3 (1:20)
How & why Drosophila became the experimental model of choice in Morgan's laboratory.

Biography


 

Thomas Hunt Morgan was one of the first true geneticists. He and his "Fly group" made tremendous contributions to our understanding of the role of chromosomes and genes in inheritance.

THOMAS HUNT MORGAN (1866-1945)

Thomas Hunt Morgan was born in Lexington, Kentucky. As a young boy, Morgan loved exploring the countryside collecting samples of wild life and fossils. At the State University of Kentucky, Morgan's course load was heavy in the natural sciences. In 1886, after graduating from State, he went to Johns Hopkins University, a relatively new school at the time, to do graduate work in zoology. His doctoral dissertation was a thorough and well-respected investigation of the embryology of sea spiders. From 1891-1904, Morgan was a professor at Bryn Mawr College where he taught biology and other natural science subjects. He continued his own research, and published books and papers on embryology and zoology.

In 1904, he was asked by his good friend, Edmund Wilson, to join the staff at Columbia University as Professor of Experimental Zoology. Morgan accepted, and so began the Drosophila chapter of Morgan's life.

Morgan had become interested in species variation, and in 1911, he established the "Fly Room" at Columbia to determine how a species changed over time. For the next 17 years, in a 16 X 23 ft. room, described by many as cramped, dusty, smelly and cockroach ridden, Morgan and his students did ground-breaking genetic research using Drosophila melanogaster, fruit flies. Though initially against the idea that the behavior of chromosomes can explain inheritance, Morgan became the leading supporter of the idea. Morgan and his students (Alfred Sturtevant, Calvin Bridges, Hermann Muller and others), developed the ideas, and provided the proof for the chromosomal theory of heredity, genetic linkage, chromosomal crossing over and non-disjunction.

Many who knew Morgan described him as an energetic, congenial man with a sense of humor and a flair for practical jokes. In the lab, Morgan was the ideas man and the planner, "the boss." He frequently left the details of planning the experiments to his "boys," his students. Morgan did do his share of work in the lab though he was resistant to the "new" equipment and methods that Calvin Bridges introduced, such as the binocular microscope. Morgan's data, often scribbled on the back of old envelopes or scraps of paper, were decorated with fly corpses. Morgan squashed "unwanted" flies rather than dumping them into the etherized morgue that Bridges set up.

In 1928, Morgan moved to Pasadena to organize the biology division at the California Institute of Technology. He became less involved with Drosophila work and returned to his earlier interests in embryology.

In 1933, Thomas Hunt Morgan received the Nobel Prize for Medicine for his work in establishing the chromosomal theory of inheritance. He shared the prize money with his children, and those of his long-time colleagues, Alfred Sturtevant and Calvin Bridges. Although Morgan officially retired from his position at Cal Tech in 1941, he continued to work in the lab until his death in 1945.

Factoid

Links


 

Links

The Interactive Fly

This site has a nice collection of pictures and images of Drosophila in various stages of development. It also has summaries of different Drosophila genes known to affect development.

A Gene Map of the Human Genome

This site put up by the National Center for Biotechnology Information has the gene maps of human chromosomes based on current information from the Human Genome Project.

Bibliography

  • Allen, Garland E., 1978, Thomas Hunt Morgan: The Man and His Science, Princeton University Press, Princeton, New Jersey.

  • Glass, Bentley, 1988, A Guide to the Genetics Collections of the American Philosophical Society, American Philosophical Society Library, Philadelphia.

  • Moore, John A., 1985, Science as a Way of Knowing, American Society of Zoologists, Thousand Oaks.

  • Portugal, Franklin H., and Cohen, Jack S., 1977, A Century of DNA: A History of the Structure and Function of the Genetic Substance, The Massachusetts Institute of Technology, Cambridge, Massachusetts.

  • Stubbe, Hans, 1972 (English Translation), History of Genetics, The Massachusetts Institute of Technology, Cambridge, Massachusetts.

  • Sturtevant, A. H., 1965, A History of Genetics, Harper & Row, Publishers, New York.

Glossary


Chromosome - One of the threadlike "packages" of genes and other DNA in the nucleus of a cell. Different kinds of organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes, 46 in all: 44 autosomes and two sex chromosomes. Each parent contributes one chromosome to each pair, so children get half of their chromosomes from their mothers and half from their fathers.
Dominant - A gene that almost always results in a specific physical characteristic, for example, a disease, even though the patient's genome possesses only one copy. With a dominant gene, the chance of passing on the gene (and therefore the disease) to children is 50-50 in each pregnancy.
Gene - The functional and physical unit of heredity passed from parent to offpsring. Genes are pieces of DNA, and most genes contain the information for making a specific protein.
Recessive - A genetic disorder that appears only in patients who have received two copies of a mutant gene, one from each parent.
Sex-linked - Located on the X chromosome. Sex-linked (or x-linked) diseases are generally seen only in males.

Children resemble their parents.
Genes come in pairs.
Genes don't blend.
Some genes are dominant.
Genetic inheritance follows rules.
Genes are real things.
All cells arise from pre-existing cells.
Sex cells have one set of chromosomes; body cells have two.
Specialized chromosomes determine gender.
Genes get shuffled when chromosomes exchange pieces.
Evolution begins with the inheritance of gene variation.
Mendelian laws apply to human beings.
Mendelian genetics cannot fully explain human health and behavior.
DNA and proteins are the molecules of the cell nucleus.
One gene makes one protein.
A gene is made of DNA.
Bacteria and viruses have DNA too.
The DNA molecule is shaped like a twisted ladder.
A half DNA ladder is a template for copying the whole.
RNA is an intermediary between DNA and protein.
DNA words are three letters long.
A gene is a discrete sequence of DNA nucleotides.
The RNA message is sometimes edited.
Some viruses store genetic information in RNA.
RNA was the first genetic molecule.
Mutations are changes in genetic information.
Some types of mutations are automatically repaired.
A chromosome is a package for DNA.
Higher cells incorporate an ancient chromosome.
Some DNA does not encode protein.
Some DNA can jump.
Genes can be turned on and off.
Genes can be moved between species.
DNA responds to signals from outside the cell.
Different genes are active in different kinds of cells.
Master genes control basic body plans.
Development balances cell growth and death.
A genome is an entire set of genes.
Living things share common genes.
DNA is only the starting point for understanding human biology.
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