Download Gregor Mendel

GREGOR MENDEL
Read the following article about Mendel and answer the questions that follow.
The folklore concept that heredity is passed on through our blood is reflected in a number of common terms,
such as “bloodlines,” “half blood,” mixed blood,” “bad blood,” “blue blood,” and “blood relative.” Once again, we
can look to Aristotle for the origin of this mistaken belief, yet it was accepted through the 19 th century by
most biologists, including Darwin. (Ironically, red blood cells are the only cells in our bodies that do not contain
genes, since those cells have no nuclei.) Gregor Mendel (1822-1884) played a pivotal role in dispelling the old
beliefs about inherited traits and establishing the study of heredity as a biological science. Imagine working
for eight years on a scientific project, spending thousands of hours preparing your data. You publish your work
and the whole scientific community ignores it. Strangely enough, this is what happened to Gregor Mendel, now
known as the Father of Genetic Science. It wasn’t until 34 years after his work was originally published, 16
years after his death, that his work was rediscovered. It has since become the basis for one of the most
significant branches of science.
Born in Heinzendorf, Austria, Mendel was the son of impoverished peasant parents, and developed an interest
in agriculture in his youth on the small family farm and orchard. He entered the Augustinian monastery in Brno
in 1843 and was ordained a priest four years later. The Augustinians paid for and supported his continued
interest in the natural sciences, sending him to the University of Vienna, where he studied physics, chemistry,
mathematics, zoology, and botany. He returned to Brno in 1854 and began to teach natural science at the high
school, where several colleagues were engaged in scientific pursuits and later founded the Natural Science
Society. Mendel joined that group and was able to expand on his particular interest in botany through the many
science books available at the school and monastery libraries.
Mendel began his experiments in breeding peas in 1854. Abbot Napp supported Mendel’s work, and built a large
greenhouse just for him to use. Mendel spent the first two years breeding strains of the common garden pea
Pisum; he wanted to make sure he had parent plants that would breed true. His goal was to discover the laws
that governed the inheritance of specific traits. The leading theory at the time was that offspring inherited a
blending of traits, that specific traits were not handed down unaltered, but that the parents’ traits were
blended together to produce something new in the offspring.
Mendel’s work was very painstaking. After breeding the true parent strains, he had to produce offspring whose
inherited traits he could trace. The pea plant he was working with had seven distinct characteristics: (1) seed
shape : angular [wrinkled] or round; (2) seed color : green or yellow: (3) seed coat color: white or gray; (4)
shape of pod : smooth or bumpy; (5) color of unripe pod : green or yellow; (6) location of flowers : tip of plant
[terminal] or along whole stem [axial]; and (7) height: tall or dwarf . Each of these traits is very distinct and
easy to see, so by using the pea plant, Mendel had picked the perfect organism for his experiments.
In May of 1856, Mendel began his actual experiments. He first crossbred the parent plants for shape - one
parent with wrinkled seeds, one with round seeds. Pea plants each contain both male and female parts. In order
to make sure he was crossbreeding only the plants he wished to, and not contaminating his experiment, he went
down one row of plants and peeled open the buds to reveal the stamen, the male part of the plant. He carefully
removed the stamen, making the plant female only, and then covered each bud with a little calico cap, to
prevent it being disturbed. A few days later, he took pollen from the male part of the plants from another row,
and fertilized the female plants. Using a paintbrush to do this, he moved a few grains of pollen at a time from
one plant to the other. He then covered the pollinated plants with little calico caps. Mendel harvested the
resulting seeds, and prepared for the second generation of plants.
In 1857, he developed the routine he would follow for the next several years: plant the seeds, fertilize the
plants, harvest, and count the offspring. Mendel first had to harvest the pods and put them in bags, making a
note of which row and plant they came from. He then popped open the pods, classifying the traits of each
seed, noting which plants they came from and replacing them in their bags. The first year he counted more
than 7000 peas, classifying each one by shape. He discovered that the ratio of round to wrinkled in these
second-generation peas was 3:1. When he re-sorted these peas by color, keeping very meticulous records of
the parent plants, he found the same ratio of yellow to green, 3:1. Mendel was a patient, thorough worker. At
the end of seven years he had repeated his experiments many times, ultimately counting over 300,000 peas. By
1863, his experiments were complete. Mendel’s genius was achieved by hard work and meticulous record
keeping, what Thomas Edison described as "1% inspiration, and 99% perspiration".
From his work, Mendel discovered that traits are transmitted independently of each other and that each
parent hands down one gene (he did not use this term) for each trait in its offspring. He discovered that of
the genes, one is dominant and one recessive for each trait. For example, with the peas, the gene for round
shape is dominant, so if one parent contributes a gene for round shape, and the other gene is for wrinkled
shape, these offspring will be round. To have a wrinkled offspring, a recessive trait, both parents must
contribute the gene for wrinkled shape. This helped describe why both constancy and variability occur in
offspring. While not using the terms we use today, Mendel was developing the General Laws of Inheritance.
In 1865 (six years after publication of Darwin’s The Origin of Species) Mendel presented two papers (titled
“Experiments with Plant Hybrids”) to the Natural Science Society in Brno, explaining the results of his pea
plant research. Yet, no one in this learned body recognized the application that Mendel’s findings could have to
understanding inheritance or evolution. Mendel even pointed out to them that no scientist had previously made
it possible “to determine the number of different forms under which the offspring of hybrids, appear, or….to
ascertain their statistical relations.” To other members of the society, his work was mathematics, which they
thought had little application to botany or natural philosophy. His paper was published in 1866 along with the
other proceedings of the society for the previous year, and copies of the entire volume were routinely
distributed to academic libraries in London, Paris, Vienna, Berlin, Rome and other major cities throughout
Europe, as well as in the United States. Mendel’s paper went largely unread and unnoticed, except by the
church’s stance on evolution. The last eighteen years of Mendel’s life were uneventful from a scientific point of
view. He returned to his monastic work, was elected abbot of his monastery in 1868, and was honored and
respected for other work in the community. Meanwhile, his revolutionary paper lay dormant on obscure library
shelves in those cities throughout the world.
Questions
1. When and where was Mendel born?
2. When did Mendel become a monk? How did becoming a monk help Mendel pursue his interest in the sciences?
At the University what did Mendel study?
3. What year did Mendel begin his experiments in pea breeding? What is the scientific name of the common
garden pea?
4. What was the leading theory at the time about inheritance?
5. List the seven traits of the pea plant that Mendel studied.
6. It took Mendel two years to create parent plants that bred “true”. What does true breeding mean?
7. Briefly explain how Mendel cross bred the parent plants.
8. What was Mendel’s routine that he developed and followed for all of his experiments?
9. In his eight years of experiments on peas, how many peas did Mendel count?
10. What did Mendel conclude from his work?
11. When did Mendel publish his work and what were his papers called?
12. What were some reasons that his papers were not taken seriously by fellow scientists and lay dormant on
library shelves until they were rediscovered in 1903?
13. How many years after he died did scientists unearth his important work and take it seriously?