Mendel’s Pea Plants
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
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Printed: January 4, 2015
AUTHORS
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
www.ck12.org
C HAPTER
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Chapter 1. Mendel’s Pea Plants
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Mendel’s Pea Plants
Define genetics.
Describe the importance of Gregor Mendel.
Explain why Mendel studied pea plants.
Distinguish self-pollination from cross-pollination.
What’s so interesting about pea plants?
These purple-flowered plants are not just pretty to look at. Plants like these led to a huge leap forward in biology. The
plants are common garden pea plants, and they were studied in the mid-1800s by an Austrian monk named Gregor
Mendel. With his careful experiments, Mendel uncovered the secrets of heredity, or how parents pass characteristics
to their offspring.
You may not care much about heredity in pea plants, but you probably care about your own heredity. Mendel’s
discoveries apply to you as well as to peas—and to all other living things that reproduce sexually.
Mendel and His Pea Plants
People have long known that the characteristics of living things are similar in parents and their offspring. Whether it’s
the flower color in pea plants or nose shape in people, it is obvious that offspring resemble their parents. However, it
wasn’t until the experiments of Gregor Mendel that scientists understood how characteristics are inherited. Mendel’s
discoveries formed the basis of genetics, the science of heredity. That’s why Mendel is often called the "father of
genetics." It’s not common for a single researcher to have such an important impact on science. The importance of
Mendel’s work was due to three things: a curious mind, sound scientific methods, and good luck. You’ll see why
when you read about Mendel’s experiments.
An introduction to heredity can be seen at http://www.youtube.com/watch?v=eEUvRrhmcxM (17:27).
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MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/277
Gregor Mendel was born in 1822 and grew up on his parents’ farm in Austria. He did well in school and became
a monk. He also went to the University of Vienna, where he studied science and math. His professors encouraged
him to learn science through experimentation and to use math to make sense of his results. Mendel is best known
for his experiments with the pea plant Pisum sativum (see Figure 1.1). You can watch a video about Mendel and his
research at the following link: http://www.metacafe.com/watch/hl-19246625/milestones_in_science_engineering_
gregor_mendel_and_classical_genetics/ .
FIGURE 1.1
Gregor Mendel. The Austrian monk Gregor Mendel experimented with
pea plants. He did all of his research in the garden of the monastery
where he lived.
Blending Theory of Inheritance
During Mendel’s time, the blending theory of inheritance was popular. This is the theory that offspring have a blend,
or mix, of the characteristics of their parents. Mendel noticed plants in his own garden that weren’t a blend of the
parents. For example, a tall plant and a short plant had offspring that were either tall or short but not medium in
height. Observations such as these led Mendel to question the blending theory. He wondered if there was a different
underlying principle that could explain how characteristics are inherited. He decided to experiment with pea plants
to find out. In fact, Mendel experimented with almost 30,000 pea plants over the next several years! At the following
link, you can watch an animation in which Mendel explains how he arrived at his decision to study inheritance in
pea plants: http://www.dnalc.org/view/16170-Animation-3-Gene-s-don-t-blend-.html .
Why Study Pea Plants?
Why did Mendel choose common, garden-variety pea plants for his experiments? Pea plants are a good choice
because they are fast growing and easy to raise. They also have several visible characteristics that may vary. These
characteristics, which are shown in Figure 1.2, include seed form and color, flower color, pod form and color,
placement of pods and flowers on stems, and stem length. Each characteristic has two common values. For example,
seed form may be round or wrinkled, and flower color may be white or purple (violet).
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Chapter 1. Mendel’s Pea Plants
FIGURE 1.2
Mendel investigated seven different characteristics in pea plants. In this chart, cotyledons refer to the tiny leaves
inside seeds. Axial pods are located along the stems. Terminal pods are located at the ends of the stems.
Controlling Pollination
To research how characteristics are passed from parents to offspring, Mendel needed to control pollination. Pollination is the fertilization step in the sexual reproduction of plants. Pollen consists of tiny grains that are the male
gametes of plants. They are produced by a male flower part called the anther (see Figure 1.3). Pollination occurs
when pollen is transferred from the anther to the stigma of the same or another flower. The stigma is a female part
of a flower. It passes the pollen grains to female gametes in the ovary.
FIGURE 1.3
Flowers are the reproductive organs of
plants. Each pea plant flower has both
male and female parts.
The anther is
part of the stamen, the male structure
that produces male gametes (pollen). The
stigma is part of the pistil, the female
structure that produces female gametes
and guides the pollen grains to them.
The stigma receives the pollen grains and
passes them to the ovary, which contains
female gametes.
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Pea plants are naturally self-pollinating. In self-pollination, pollen grains from anthers on one plant are transferred
to stigmas of flowers on the same plant. Mendel was interested in the offspring of two different parent plants, so he
had to prevent self-pollination. He removed the anthers from the flowers of some of the plants in his experiments.
Then he pollinated them by hand with pollen from other parent plants of his choice. When pollen from one plant
fertilizes another plant of the same species, it is called cross-pollination. The offspring that result from such a cross
are called hybrids.
Summary
• Gregor Mendel experimented with pea plants to learn how characteristics are passed from parents to offspring.
• Mendel’s discoveries formed the basis of genetics, the science of heredity.
• Cross-pollination produces hybrids.
Making Connections
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/45552
Explore More
Explore More I
Use this resource to answer the questions that follow.
• Children resemble their parents at http://www.dnaftb.org/1/bio.html .
1. What did Gregor Mendel discover about "factors", which are genes?
2. Briefly state Mendel’s three laws.
Explore More II
• Gregor Mendel and pea plants at http://www.dnalc.org/view/16002-Gregor-Mendel-and-pea-plants.html .
Review
1.
2.
3.
4.
What is the blending theory of inheritance? Why did Mendel question this theory?
List the seven characteristics that Mendel investigated in pea plants.
How did Mendel control pollination in pea plants?
What are hybrids?
References
1. William Bateson. Gregor Mendel portrait . Public Domain
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Chapter 1. Mendel’s Pea Plants
2. Rupali Raju. Summary of the characteristics Mendel studied . CC BY-NC 3.0
3. Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation. Parts of a flower . CC BY-NC 3.0
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