Gregor Mendel's Influences for his Pea-Plant Experiments

By Abigail Cardinal, Danielle Kelly, Courtney Knapp, Mohammed Scruggs

Biography 

Gregor MendelGregor Johann Mendel was born on July 20th, 1822 in the Austrian Empire, now the Czech Republic.

He was an Augustinian friar of the Catholic church and a scientist. He eventually became the abbot of St. Thomas' Abbey, after which his scientific work decreased due to increasing administrative responsibilities. Mendel is known for pea-plant experiments and subsequent theories on genetics. During a seven year period, Mendel experimented with pea plants in the garden owned in his monastery. 

Mendel also worked with bees to determine genetic traits in animals. Mendel’s work was not widely recognized until after his death in 1884. 

There were several factors that influenced Mendel's theories, such as society, his interest in science, previous work by other scientists,and religion.


Mendel's Influences 

Influences in science is one of the most fundamental questions in recording the history of science: each scientist is almost always inspired by earlier work. In his book about well known biologist, (including Mendel), Berger highlights the importance of inspiration by claiming that a scientists' discovery relies on the discovery made by another scientists' previous and similar work.[1]  Mendel's influences are therefore importance because they can shed light onto his motivations, techniques, choices, and ultimate success in the field of hereditary science.


As a child, Mendel attended a school in which natural sciences were emphasized and the students learned importance of beekeeping and how to grow fruit.[2]  Indeed, Mendel would be interested in beekeeping well into adulthood and completed a series of experiments at his monastery later in life.   


Although Mendel's pea plant experiments revolutionized the discussion on genetics, a similar discussion on hybridization and breeding had been taking place for nearly 100 years before Mendel. Mendel had been taught about hybridization during his early school days and was influenced by both past scientists and colleagues. 

Mendel attended the University of Olomouc and was likely influenced by Johann Karl Nestler, a scientist interested in hereditary traits and agriculture, who taught there. 


Karl Nestler emphasized selective breeding in sheep: he encouraged sheep breeders to be more exclusive when selecting sheep to breed to include wool quality. Nestler tried to explain the importance of careful breeding, by noting that nature is capable of producing species of animals and plants through forces man and that breeders control the reproductive process, such as inbreeding or outcrossing.[3] These themes can be seen through Mendel's work: he sought to articulate the way in which breeders could control traits and why. 

After university, Mendel taught at Br
ünn Modern school. Another teacher, Alexander Makowsky, specialized in botany and geology. He and Mendel became close associates. Makowsky's special area of interest was the study of flowers, which may have inspired Mendel to look at plants in order to determine hereditary likelihood. 

K. Gaertner's Experiments and Observations upon Hybridization in the Plant Kingdom was found among Mendel's
 possessions after his death. The book was filled with Mendel's notes. Gartner worked with plants in his experiments, including peas, which may have inspired Mendel to work with the same plant.[4]  Pea plants were a common and good choice for hybridization experiments because they normally self-pollinate.   

Historian Colleen Huckabee notes the way in which Mendel's experiments were not unusual: Scientists Knight, Gross and Seton had already discovered dominant and recessive traits and the "segregation into yellow and green... seedlings of hybrid parents."[2] Mendel undoubtably worked off their original experiments. However, he was successful because he focused on each trait individually and with true breeding plants. He also used algebra to articulate and prove patterns of inheritance.[2]

Mendel also owned Darwin's Origin of Species, which had been translated in German by 1860. It seems likely that Mendel originally intended his pea experiments to show that variability in offspring is caused by parental influence; Darwin had suggested that variability occurs when there is an environmental change.[4] Mendel's disagreement with Darwin's theory might have occurred because of his religious background.
 

These scientists and their work on hybridization of plants are important because they set up groundwork on the relationship between plants and offspring, and their works were found among Mendel's possessions. Mendel likely continued with pre-established plant experiments because they simply interested him: both his early schooling and his monastery encouraged scientific thought and experimentation.  Mendel was unaware of the significance of his pea-plant experiments in the study and development of modern hereditary theory. 

Influences from Religion

Gregor Mendel was recommended by a priest to enter the monastery.  While in the monastery, he spent years studying Greek, Hebrew, pedagogical methods, and theology and became an Ausustinian Monk.[5] Ideas and theories that Darwin was presenting at the time, he did not believe because he believed God was the creator of all life.  In 1874, Mendel was so devoted to the monastery that he fought the government for 10 years (until his death) who wanted to impose a national tax on monastic property.[6]  After joining the monastery, he became devoted to religion and believing God was the creator of life, which challenged Darwin and other evolutionists of the time. During his studies, Mendel became close to one of his teachers Monk F.M. Ladimir Klacel, who shared his interests in religion, evolution and society.[7] Being surrounded by other Monks with the same beliefs only strengthened them. 

Plant Hybridization Experiments

Gregor Mendel conducted hybridization experiments on around 29,000 pea plants. Peas were an ideal choice for Mendel to use because they had easily observable traits there were 7 of which he could manipulate. He began his experiments on peas with two conditions. The conditions were 1) possess constant differentiating characteristics and 2) hybrids of such plants, during flowering period, be protected from the influence of all foreign pollen.[8] The second condition was used to protect from an accidental impregnation thus would cause misleading results. Mendel planned to selectively cross pollinate the peas with one another to study the traits passed on and the results from each pollination. He acquired about 34 varieties of peas and chose 22 different types to conduct his experiments with which varied in color and size.[8] He took years of breeding constant family lines to perfect the original constant traits. Mendel used seven pea plant traits in his experiments which include flower color (purple or white), flower position (axil or terminal), stem length (long or short), seed shape (round or wrinkled), seed color (yellow or green), pod shape (inflated or constricted), and pod color (yellow or green). The first generation of the hybrids produced a 3:1 ratio where there were 3 plants showing dominant traits and 1 showing recessive.[8] The second generation produces a 2:1:1 ratio. This showed there was one with the recessive trait, two with hybrid trait and one with dominant trait.

When crossing a green pod plant and a yellow pod plant, the first generation (F1) would produce only green plants (given green was the dominant trait color. But then the second generation (F2) produced a quarter yellow pea pods. These experiments allowed Mendel to conclude on two laws of Inheritance; the Law of Segregation and the Law of Independent Assortment.

 

Mendel and the Pea Plant

The Principle/Law of Segregation, Mendel’s “First Law”

Mendel concluded on this law after finding when breeding white and purple colored flowered plants it was not a mix of the two colors, but really one color was chosen over the other. There are four different parts of the law he included

1)   There are other forms of genes that can determine the heritable traits, alleles.

2)   Each offspring receives one allele from each parent.

3)   Either a sperm or egg holds only one allele for each trait and those pair during fertilization.

4)   If the alleles are different one is seen and the other is not as one trait is dominant and the other is recessive.

The law is a direct result from watching the production of the F2 generation and the production of the 2:1:1 ratio. The recessive traits only came when those were the only two being bred with each other. His conclusions were easily observed

 

The Principle/Law of Independent Assortment, Mendel’s “Second Law”

Mendel decided different pairs of alleles are passed on as individuals and not based upon each other. Mendel saw various combinations, which indicated all of the alleles are segregated from one another. When Mendel began mixing two traits and conducting dihybrid crosses he found a 9:3:3:1 ratio. Unless the traits are linked he concluded various traits are inherited independently and have no relation. 




Publication 

Between 1856 and 1863, Mendel experimented on thousands of pea plants.  During the seven years of conducting experiments on pea plants, Mendel experimented with a variation of different breeding techniques by using pea plants with different traits and recording the results of their offspring. 

As Mendel began his now-famous pea-plant experiments, earlier scientists had already used hybridization to study plants and traits.  These men were inspired by Linnaeus’s idea that “new species might be generated by the hybridization of new ones.”[9]  As a Catholic priest who was not a believer of Darwinism, Mendel took a renewed approach to hybridization.  He wanted to “establish the laws of hybridization, not the laws of heredity.”[9] Because other scientists, such as Linnaeus, were already establishing theories about hybridization, Mendel's experiments seemed little more than further evidence for pre-established hybridization theories.  
Mendel himself wasn't aware of the potential impact of his work; he wrote little to suggest he fully understood the implications of his findings and did little to promote his work, other than have it published in a local paper.  

In 1865, Mendel gave two lectures to mostly scientists and former peers about his discoveries from his pea plant experiments.  The first lecture given on February 8th consisted of mostly mathematical ratios that left famed botanist Alexander Makowsky, chemist Franz Czermak and physician Jacob Kalmus confused.[10]  Four weeks later, he gave his second part of the lecture to the same audience, and like the first time, scientists and Mendel's peers were still confused about the pea plant experiments, and if they had any significance.  In the town of Brünn, where the lecture was given, the newspaper Tagesbote published an article that summarized Mendel’s lectures.  Unless the newspaper headmaster Josef Auspitz understood Mendel’s lectures enough to write about them, it is speculated that Mendel himself wrote the article.[10]  Mendel's lectures were published into a paper called "Experiments on Plant Hybridization" in 1866.  The paper was widely ignored because illegitimacy of the journal his paper was published in.  It was reproduced in a couple of other papers. Mendel also presented his paper to the Natural History Society of Brunn. However, most felt Mendel's work was a further study of hybridization, rather than about hereditary theory. It was therefore widely ignored by the scientific community. 

Mendel's work challenged pre-established thoughts about hybridization, hereditary patterns and the connections between the two: “Unit characters were incompatible with the whole theoretical framework within which most biologists thought about heredity and development."[9]

Primarily, Mendel’s work was neglected by scientists because it proposed a completely new model of heredity.  Scientists were confused by his experiments unless they were deciphered in terms of unit characters, which “were incompatible with the whole theoretical framework within which most biologists thought about heredity and development.”[9] Unit characters were explained by a material particle that transmitted from generation to generation.  Nowhere in the paper does Mendel mention paired material particles, as he mostly explained in terms of character differences and provided no hypothesis about how the differences are maintained.  This unclear information caused a lot of confusion among scientists and others who read Mendel's paper.  Second, the journal Proceedings of the Natural History Society of Brünn which published Mendel’s paper was questioned by scientists; it was very obscure.

Mendel’s paper was ignored by all scientists except one, Carl von Nageli, a botanist.  Carl von Nageli suggested to Mendel to experiment with hawkweed plants, which had complex genetics that defied analysis by these techniques.  Mendel and von Nageli discovered that they could not replicate the findings because the hawkweed plant reproduces asexually from diploid tissue in the ovary, therefore producing clones of the parent.

Rediscovery of Mendel’s Work

The rediscovery of Mendel’s work occurred almost twenty years after his death in the early twentieth century.  What sparked this new found interest in Gregor Mendel among the science community thirty fours after the publication of his work? The year 1900 marked the beginning of the modern period in the study of heredity. Before the twentieth century, Mendel received heavy criticism on his work and was almost completely ignored when his work was first published. The criticism he received was that “the clearly distinct character states he studied in his peas are not typical of most species, so his work would have seemed only an exception to the rule."[9]

During this era, the growth of the eugenics movement focused public attention on heredity as a source of degenerate characters in the human population. Mendel did not anticipate that the results of his work would be used as the basis for thinking about heredity. It is often believed that he may not have been testing heredity after all which explains why no one understood his new “theory of heredity” at the time because there was no such theory. Rather, he was really trying to substantiate an alternative to Darwin’s theory of evolution.[9]

The new emphasis on biology in the early twentieth century was in part a response to more general changes taking place in society.  These changes would set the scene for the rediscovery of Mendel’s laws.  The scientists who initially rediscovered Mendel's work in the 1900s was Hugo Marie de Vries, Carl Correns and Erich von Tschermark.  von Tschermark efforts in trying to understand Mendel's work is now largely rejected because he was still unclear himself about Mendel's laws.  de Vries and Correns had been conducting hybridization experiments in 1900 and reported the laws of transmission already noted by Mendel. After finding that mutated characters did not necessarily follow Mendel's laws, de Vries soon lost interest in Mendelsim.  William Bateson was an English geneticist, had an interest in Mendelism.  Bateson was impressed with Mendel’s paper and produced the first English translation and made the argument that it should be used as the basis for a new science of heredity. 

In 1905, Bateson coined the term “genetics”, which he previewed at an international congress, attempting to promote the new science at Cambridge University.[11] Meanwhile in the United States, this new science known as genetics was becoming popular among agricultural interests  and was easily established in the US because the university system began to expand at this this time.



References

1. Berger, Melvin. 1968. Famous men of modern biology (pp.114-131). New York: Y. Crowell, Co.

2. Huckabee, Colleen J. 1989. Influences on Mendel (pp.85). Berkeley: The American Biology Teacher and University of California Press.

3. Engels, Eve Marie. 2008. The reception of Charles Darwin in Europe (pp.239). New York: Continuum International Publishing Group.

4. Olby, Robert C. Origins of Mendelism (pp. 17-54). New York: Schocken Books. 

5. Graves, Dan. 1996. Scientists of faith (pp.46-48)Grand Rapids: Kregel Resources.

6. Raymond J. Seeger. 1985. Kepler, peaceful Protestant (pp.93-96)Ipswich: The Journal of the American Scientific Affiliation.

7. Peaslee, Margaret H., and Vitezslav Orel. 2007. The evolutionary ideas of F. M. (Ladimir) Klacel, teacher of Gregor Mendel (pp/151-156). Czech Republic: Biomed Pap Med Fac. Univ. Palacky Olomouc. 

8. Mendel, Gregor. 1865. Experiments in plant hybridization (pp.1-39)Brünn: Proceedings of the Natural History Society of Brünn

9. Bowler, Peter J., and Iwan Rhys Morus. 2005. Making modern science: a historical survey (pp.153,196-199). Chicago: University of Chicago.

10. Henig, Robin Marantz. 2000. The monk in the garden: the lost and found genius of Gregor Mendel, father of genetics (pp. 135-136). New York: Mariner Books.

11. Bateson, William. 1909. Mendel's principles of heredity (pp.7-17). London: Cambridge University Press.

Video: Mendel and the Pea Plant. October 27, 2010. http://www.youtube.com/user/whatcatiesaid/videos



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