Concept

Since the beginning of human history, people have wondered how traits are inherited from one generation to the next. Although children often look more like one parent than the other, most offspring seem to be a blend of the characteristics of both parents. Centuries of breeding of domestic plants and animals had shown that useful traits — speed in horses, strength in oxen, and larger fruits in crops — can be accentuated by controlled mating. However, there was no scientific way to predict the outcome of a cross between two particular parents. It wasn't until 1865 that an Augustinian monk named Gregor Mendel discovered that individual traits are inherited as discrete "factors," which later became known as genes. His rigorous approach transformed agricultural breeding from an art to a science. He started with parents of known genetic background — to provide a baseline against which to compare patterns of inheritance in the resulting offspring. Then he carefully counted the traits found in successive generations of offspring.

Animation

Hello, I'm Gregor Mendel. I worked with pea plants because they are easy to grow and they have many variable traits. Most importantly, they can be crossed with themselves or other pea plants. When left alone, pea flowers self fertilize. Let's look inside... The stamens, the male sex parts, mature first and drop pollen inside the immature flower. The pistil, the female sex part, matures later. Its eggs are fertilized by the pollen that lands on the pistil. To cross fertilize pea plants, I opened the immature flower. Then, I cut off the stamens before they matured and dropped pollen. After the flower matured, I dusted its pistil with pollen from another plant. This is cross fertilization.

Gallery

Mid-1800s French caricature by Honore Daumier titled "Un Nouveau Nez," translated "A New Nose". Some human traits were thought to be inherited.

1832 caricature titled "A Chip off the Old Block". Some human traits were incorrectly thought to be inherited.

Thomas Hunt Morgan (1933 winner of the Nobel Prize for Medicine for his work on the chromosomal theory of inheritance), with his daughters, Isabel (left) and Lilian (right), 1920.

Audio/Video

Audio Glossary

Gene, Inherited, Mendel, Johann (Gregor)

Video Interviews

Robert Olby

Professor of History Robert Olby teaches at the University of Pittsburgh, and has written several books on the history of genetics, including Origins of Mendelism and The Path to the Double Helix.

Clip 1 (0:36)
Description of Mendel's Paper.

Clip 2 (1:00)
Why should Mendel be considered the Father of Genetics?: the three main accomplishments of Mendel's paper.

Biography

JOHANN GREGOR MENDEL (1822-1884)

Father of Genetics

Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance. He deduced that genes come in pairs and are inherited as distinct units, one from each parent. Mendel tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits. He recognized the mathematical patterns of inheritance from one generation to the next. Mendel's Laws of Heredity are usually stated as:

1) The Law of Segregation: Each inherited trait is defined by a gene pair. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. Offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilization.

2) The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another.

3) The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.

The genetic experiments Mendel did with pea plants took him eight years (1856-1863) and he published his results in 1865. During this time, Mendel grew over 10,000 pea plants, keeping track of progeny number and type. Mendel's work and his Laws of Inheritance were not appreciated in his time. It wasn't until 1900, after the rediscovery of his Laws, that his experimental results were understood.

This is a site where you can get a lot of information about Gregor Mendel, his life and scientific achievements. Read Mendel's introductory remarks about his experiments and why he chose to work with pea plants. You can also read the essay written by Dr. Vítezslav Orel, Emeritus head of the Mendel museum in Brno, on how people viewed heredity before Mendel.

John Innes Centre

The John Innes Centre has a research group working on cloning pea genes. They also have pictures of Mendel's pea traits.

Bibliography

Bowler, Peter J., 1989, The Mendelian Revolution, The Athlone Press, London.
Dunn, L. C., 1965, A Short History of Genetics, McGraw-Hill, Inc., New York.
Iltis, Hugo, 1932, Life of Mendel, W. W. Norton & Company, Inc., London.
Moore, John A., 1985, Science as a Way of Knowing, American Society of Zoologists, Thousand Oaks.
Olby, Robert C., 1966, Origins of Mendelism, Constable and Company Ltd., London.
Orel, Vitezslav, 1996, Gregor Mendel, the First Geneticist, Oxford University Press, Oxford.
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.
Stern, Curt, and Sherwood, Eva R., ed., 1966, The Origin of Genetics: A Mendel Source Book, W. H. Freeman and Company, San Francisco.
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

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.
Inherited - Transmitted through genes from parents to offspring.
Mendel, Johann (Gregor) -

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.
Chromosomes carry genes.
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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