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Johann Gregor Mendel
1822 - 1884
The Moravian natural scientist and Augustinian abbot Johann
Gregor Mendel (1822-1884) laid the foundations of modern
genetics with his paper dealing with the hybridization of peas.
Gregor
Mendel was born on July 22, 1822, at Hynice, Czechoslovakia
(then Heinzendorf, Austrian Silesia). His ancestors were
farmers, and his father still had to work three days a week as a
serf. Mendel displayed a great love for nature all his life.
Years of Preparation and Education
In 1831 Mendel was sent to the Piarist school in Lipník (Leipnik)
and at the age of 12 to the grammar school in Opava (Troppau).
In 1840 he enrolled at the Institute of Philosophy in Olomouc (Olmütz).
Mendel was admitted to the Augustinian order in Brno (Brünn) in
1843. The Augustinians taught philosophy, foreign languages,
mathematics, and natural sciences at secondary schools and
universities. Abbot Napp, the head of the monastery, devoted all
his energy to the economic development of the monastery and to
the scientific education of the members of the order. Surrounded
by an atmosphere of dynamic activity, Mendel found optimum
conditions for his studies and later for his research work.
Along with his theological studies Mendel took courses in
agriculture, pomiculture, and vine growing at the Institute of
Philosophy in Brno. In 1847 he was ordained a priest and served
for a short time as vicar at the Old Brno Monastery.
In 1849 Mendel became a teacher of mathematics and Greek at the
grammar school in Znojmo (Znaim). After a year the headmaster
recommended him for the university examination. Together with
his application for admission to the examination Mendel enclosed
his autobiography, which is the only authentic preserved
document. Mendel failed the examination, probably because he
lacked a complete university education. Only his written test on
meteorology satisfied his examiner, and, on the latter's
recommendation, Abbot Napp sent Mendel to study natural sciences
at the University of Vienna (1851-1853). He heard F. Unger
lecture on plant anatomy and physiology, the use of the
microscope, and the practical organization of experiments. Unger
was known for his views on evolution and had investigated the
problem of the origin of plant variability by means of
transplanting experiments. Mendel later performed these
experiments also. It is now assumed that Unger's views deeply
influenced Mendel in the formation of his ideas before he
performed his experiments with edible peas (Pisum).
On his return to Brno in 1854 Mendel was appointed a teacher of
physics and natural history in the Technical School. In 1856 he
prepared himself for the university examination again, but he
became seriously ill and did not take it. By this time, however,
Mendel was fully occupied with his hybridizing experiments with
Pisum. He remained a teacher till 1868, when he was elected
abbot of the monastery.
Hybridizing Experiments
Mendel started his extensive program of hybridizing experiments
in 1854. He focused his energy on the problem of the origin of
plant variability. For two years he tested the purity of
selected varieties of Pisum and then began experimenting with
artificial fertilization. A new reconstruction of Mendel's
experimental data illustrates that he must have tested about
28,000 Pisum plants during the years 1856-1863.
Mendel summarized the experimental results in a paper,
"Experiments on Plant Hybrids," which he read at two meetings of
the Natural Science Society in Brno in 1865; the paper was
published in the proceedings of the society's journal. Though
prominent natural scientists were present at the meeting, no one
understood Mendel's ideas or the significance of his work. The
proceedings were distributed to 134 scientific institutions in
Europe and the United States, but the published paper failed to
arouse interest.
Mendel's original idea, that heredity is particulate, was
contrary to the theory of "blending heredity" that was generally
accepted at that time. In the plants that Mendel tested (and in
biparental-reproducing organisms generally), the hereditary
particles (called elements by Mendel) from each parent are
members of pairs. In forming the reproductive cells, the pair
members segregate in different pollen or sperm nuclei and in
different eggs or ovules to transmit the hereditary
determinants. From one parent comes one particle determining,
for example, the round shape of the seed (A), and from the other
parent that representing the wrinkled shape (a). Mendel called
the trait passing entirely unchanged into hybrid (derived from
unlike parents) association "dominant," and the trait becoming
latent in hybrids "recessive." The particles meet (recombine) in
the offspring (Aa) but do not influence each other.
Suppose the pair members of these hybrid offspring now segregate
in forming reproductive cells, producing two types of sperm or
egg, namely Aor a, and that these particles meet at random in
fertilization. The resulting combination series of relevant
particles is: ¼ AA, ¼ Aa, ¼ aA, ¼ aa, or AA ¼2 Aa ¼ aa. That is,
there are four genetic types of offspring from the hybrids, each
type represented by 25 percent of the total. In this way, in the
hybrid progeny the parental forms appear again; after 1900 this
segregation of the hereditary units (in 1909 termed genes) was
called Mendel's law of segregation.
Mendel found that hereditary particles belonging to different
trait pairs, for example, A, a for the seed shape and B, b for
the seed coloration, formed the combination series in
recombining without influencing each other. The combination
series could be predicted by combining the simple series AA
2Aaaa; BB 2Bbbb, resulting in the combination series
AABBAAbbaaBBaabb 2AABb 2aaBb 2AaBB 2Aabb 4AaBb. In his paper
Mendel actually illustrated such a recombination in crossing
peas differing in two and three trait pairs. Expected particle
recombinations were realized in actual counts of the offspring.
The recombination of the hereditary particles was called
Mendel's law of independent assortment.
Mendel gave the impulse for his experiments in the first
sentence of his paper: "Artificial fertilization undertaken on
ornamental plants to obtain new colour variants initiated the
experiments to be discussed." His task was to find "the
generally applicable law of the formation and development of
hybrids as a way of finally reaching the solution to a question
whose significance for the evolutionary history of organic forms
must not be underestimated." In his paper he expressed the
opinion that "the distinguishing traits of two plants can, after
all, because only by differences in the composition among
grouping of the elements existing in dynamic interaction in the
primordial cells." He assumed the general validity of his theory
because, according to him, "unity in the plan of development of
organic life is beyond doubt."
Being interested in the development of hybrid forms, Mendel also
explained that the population descending from hybrids tends to
revert to the pure parental forms, resulting in diminishing the
hybrid's form. Thus, as a consequence of Mendelian segregation,
Mendel also laid the basis for the interpretation of the effect
of inbreeding.
Mendel continued his hybridizing experiments, crossing various
forms of 22 other genera of plants, to prove the general
validity of his theory in the plant kingdom. He also cultivated
wild plants in the garden with the aim of investigating
Lamarck's views concerning the influence of environment upon
plant variability; he could not agree with Lamarck. He was
convinced, like Darwin, that it was impossible to draw a
hard-and-fast line between species and varieties, and in the
conclusion of his Pisum paper he expressed the conviction that
the variability of cultivated plants could be explained by his
theory.
After 1871 Mendel also tried to carry out hybridizing
experiments with bees. He bred about 50 bee races which he tried
crossing to obtain new cultural breeds. His crossing experiments
could not be successful, however, because of the complex problem
of the controlled mating of queens. For this reason Mendel
focused his activity on research of the technological aspects of
apiculture, such as the hibernation of bees.
As a member of the Natural Science Section of the Agricultural
Society in Brno and as a respected meteorologist, Mendel
summarized the results of meteorological observations in 1856
and published them in six reports (1862-1869). He also published
three papers on extraordinary storms (1870-1872). He was a
member of the Central Board of the Agricultural Society from
1870, and he supported the first weather forecasts for farmers
in 1878. In 1861 he helped found the Natural Science Society of
Brno.
Taxation and the Monastery
After Mendel was elected abbot of the monastery in 1868, he had
little time for his experimental activities, although they never
came to a total stop. In 1874 the government proclaimed a new
law relating to the contribution of the cloisters to the
religious fund. Mendel refused to pay the high assessed taxes
and thus, from the end of 1875, got himself into trouble with
the provincial government and with the Ministry of Education in
Vienna. The result of this conflict was the lasting
sequestration of the landed monasterial property. In an attempt
to win Mendel over and stop his opposition to the taxation law,
the government appointed him to the Board of Directors of the
Moravian Mortgage Bank. In 1876 he became the vice-governor of
the bank and in 1881 the governor. Nevertheless, Mendel never
agreed to the taxation law.
The long struggle over taxation had a serious effect on Mendel's
health. He died on Jan. 6, 1884, without any public recognition
of his outstanding scientific achievements.
Contributions to Genetics
Mendel's paper of 1865 went unnoticed except for an occasional
reference in scientific literature. In 1900 it was rediscovered
by scientists, when his theory was generalized as Mendel's laws
of heredity. That date also marked the beginning of the science
of heredity, which in 1906 was named genetics. Not even after
1900 was Mendel's theory acknowledged as being generally valid,
and the Darwinian selection theory was often considered to
oppose the Mendelian theory.
Later, it was demonstrated that Mendel had also observed such
phenomena as intermediate inheritance, complete linkage,
additive gene action, and gene interaction, and that he himself
appreciated the Darwinian selection theory and refused to accept
the hypothesis of pangenesis. The synthesis of the Darwinian and
Mendelian theories was first proved by S. S. Tchetverikoff in
1926 and finally by R. A. Fisher in 1930, Sewall Wright in 1931,
and J. B. S. Haldane in 1932.
Since that time Mendel's work has been reappraised. His
hypothesis of hereditary particles turned out to be quite
general and provided the elementary principle of heredity in all
forms of life from viruses to man. From this viewpoint his laws
of heredity appear to be only the subordinate principles of
Mendel's main discovery, which furnishes proof of the existence
of genes as determining the whole character of each organism.
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Johann
Mendel, who changed his name to Gregor when he entered a
monastery as a young man, was born on his father's farm on July
22, 1822. By the time he was 11 years old, Johann had learned
everything possible from his local school. The schoolmaster
suggested that he attend a school in a larger town many miles
away. This would be difficult for Mendel's family, because he
would need to pay for room and board.
Mendel's father owned a 45-acre farm; however, the family lived
a frugal life with little money for "extras." Nevertheless,
Mendel's family found a way to send him to Leipnik School, where
he studied for one year. His teachers then recommended that
Mendel attend Troppau High School, which was 20 miles from his
home. Because money was tight, Mendel often went hungry.
However, he finished his six-year course in 1840 and graduated
with high honors.
Mendel realized that he needed additional schooling to begin a
career. Upon graduation, he enrolled at the Philosophical
Institute at Olmütz, which was 100 miles away. After two years
at the Institute, Mendel was unsure of his future. His physics
professor recommended that Mendel join St. Thomas Monastery in
Brünn, Austria, now known as Brno, Czech Republic. At the
monastery, Mendel did not have to worry about food or shelter,
and he received a fine education. In 1843, Mendel was accepted
as a trial member at the monastery, and he took his new name,
Gregor.
In 1848, Mendel was assigned as a priest, but he soon realized
that parish work was not for him. He was reassigned to a high
school teaching position and was considered a good teacher.
However, Mendel was not able to pass the teaching exam, and it
was recommended that he spend two years at the University of
Vienna at the monastery's expense. Mendel completed his studies,
but again he was unable to pass the exam.
Mendel continued to teach on a temporary basis, but he spent the
majority of his time in the monastery gardens. He developed an
interest in what we now call heredity, and he experimented with
pea plants in an attempt to prove his theories. Mendel decided
to cross-fertilize plants with opposite characteristics; such as
tall plants with short plants, and plants that produced smooth
peas with those that produced wrinkled peas. Through these
experiments, Mendel was able to set out a theory that all living
things have aspects called dominant and recessive traits.
In February 1865, Mendel presented his findings to the Natural
History Society of Brünn and published them under the title
"Experiments in Plant Hybridization" in a scientific journal. No
one seemed interested in Mendel's findings. Even when he sent
his papers to renowned University of Munich professor Karl von
Nägeli, his discoveries went unappreciated. The years passed,
and Mendel realized that his findings were not going to be
recognized in his lifetime.
In 1868, Mendel was elected Abbot and Prelate of St.Thomas
Monastery, which left him little time to continue his studies
and experiments. He led a comfortable life for the next 15
years. Gregor Mendel died on January 6, 1884 at the age of 62.
Sixteen years later, Mendel's findings were rediscovered.
In 1900, three botanists in different parts of Europe came
across his papers. Hugo de Vries, Carl Correns, and Erich
Tschermak praised Mendel's research and achieved similar results
in their own studies. Mendel's principles of heredity began to
be referred to as the Mendelian Laws, and these laws are
considered to be the foundation of the modern study of genetics.
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This web page was last updated on:
13 December, 2008
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