GREGOR MENDEL
Gregor Mendel (1822-84)
was an Austrian monk
who studied genetics.
- Heredity in plants
What is heredity?
Heredity is the passing
down of traits from one
generation to another.
Mendel’s Observations

Mendel made many observations about pea
plant characteristics.
Mendel’s Observations
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Mendel’s first series of
observations included both
tall and short plants.
He assumed that there
would be equal amounts of
each plant size if they
were crossed or mated.
Mendel’s Pea Plant Experiment
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Why did Mendel chose to study pea plants?
How did he make the plants reproduce?
What did Mendel do?

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Mendel crossed a tall plant and a short plant.
 Remember: Mendel thought that the offspring
would be half tall and half short.
Actually, all the offspring were tall!
P Generation
F1 Generation
Then what did Mendel do?

Mendel then performed a self-cross within the
offspring generation.
F1 Generation

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F2 Generation
This time, 75% of the offspring were tall and 25%
were short.
Where did the short plant come from???
R
E
C
A
P
Characteristics vs. Traits

A characteristic is the
category of traits


Hair Color is a
Characteristics
A trait is a type of the
characteristic

Brown, Red, or Blonde
Hair are Traits
What did Mendel conclude?
Mendel's observations from these
experiments can be summarized in two
principles or laws:
1. The Law of Segregation
2. The Law of Independent Assortment
Law of Segregation



An organism has two types
of each trait. Only one is
passed on to the next
generation.
Which trait is passed on is a
matter of chance.
This segregation of traits
occurs during the process of
sex cell formation
Independent Assortment


Alleles for different traits are passed to
offspring independently of each other.
Here are two examples to clear this up:
 A pea plant having purple flowers does not
mean the pea plant is tall.
 Likewise, the principle of independent
assortment explains why a person with
brown hair does not always have dimples.
Independent Assortment
Question: Can you think of any exceptions to
the law of independent assortment?
 Why do most people with red hair have
freckles?
 Why do most people with (natural) blonde
hair have light colored eyes?
Answer: Some genes are very close to each
other on the chromosome. Therefore, when one
gene is passed down, chances are, so will the
other one.