GREGOR MENDELGREGOR MENDEL Gregor Mendel (1822-Gregor Mendel (1822-

84) was an Austrian 84) was an Austrian monk who studied monk who studied genetics. genetics. - - Heredity in plantsHeredity in plants

What is heredity? What is heredity?

Heredity is the passing Heredity is the passing down of traits from one down of traits from one generation to another.generation to another.

Mendel’s ObservationsMendel’s Observations

Mendel made many observations about Mendel made many observations about pea plant characteristics. pea plant characteristics.

Mendel’s ObservationsMendel’s Observations

Mendel’s first series of Mendel’s first series of observations included observations included both tall and short both tall and short plants.plants.

He assumed that there He assumed that there would be equal would be equal amounts of each plant amounts of each plant size if they were size if they were crossed or mated.crossed or mated.

Mendel’s Pea Plant Mendel’s Pea Plant ExperimentExperiment

Why did Mendel chose to study pea Why did Mendel chose to study pea plants?plants?

How did he make the plants reproduce?How did he make the plants reproduce?

What did Mendel do?What did Mendel do? Mendel crossed a tall plant and a short plant.Mendel crossed a tall plant and a short plant.

Remember: Mendel thought that the Remember: Mendel thought that the offspring would be half tall and half short.offspring would be half tall and half short.

Actually, all the offspring were tall! Actually, all the offspring were tall!

P Generation F1 Generation

Then what did Mendel do?Then what did Mendel do? Mendel then performed a self-cross within the Mendel then performed a self-cross within the

offspring generation. offspring generation.

This time, 75% of the offspring were tall and This time, 75% of the offspring were tall and 25% were short.25% were short.

Where did the short plant come from???Where did the short plant come from???

F1 Generation F2 Generation

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Characteristics vs. TraitsCharacteristics vs. Traits

A characteristic is A characteristic is the category of traitsthe category of traits Hair Color is a Hair Color is a

CharacteristicsCharacteristics A trait is a type of A trait is a type of

the characteristicthe characteristic Brown, Red, or Brown, Red, or

Blonde Hair are TraitsBlonde Hair are Traits

What did Mendel conclude?What did Mendel conclude?

Mendel's observations from these Mendel's observations from these experiments can be summarized in experiments can be summarized in two principles or laws:two principles or laws:

1. The Law of Segregation1. The Law of Segregation

2. The Law of Independent 2. The Law of Independent AssortmentAssortment

Law of SegregationLaw of Segregation An organism has two An organism has two

types of each trait. Only types of each trait. Only one is passed on to the one is passed on to the next generation.next generation.

Which trait is passed on Which trait is passed on is a matter of chance.is a matter of chance.

This segregation of traits This segregation of traits occurs during the process occurs during the process of sex cell formationof sex cell formation

Independent AssortmentIndependent Assortment

Alleles for different traits are passed to Alleles for different traits are passed to offspring independently of each other. offspring independently of each other. 

Here are two examples to clear this up:Here are two examples to clear this up: A pea plant having purple flowers A pea plant having purple flowers

does not mean the pea plant is tall.does not mean the pea plant is tall. Likewise, the principle of independent Likewise, the principle of independent

assortment explains why a person assortment explains why a person with brown hair does not always have with brown hair does not always have dimples.dimples.

Independent AssortmentIndependent Assortment

Question: Can you think of any exceptions Question: Can you think of any exceptions to the law of independent assortment?to the law of independent assortment? Why do most people with red hair have Why do most people with red hair have

freckles?freckles? Why do most people with (natural) Why do most people with (natural)

blonde hair have light colored eyes?blonde hair have light colored eyes?

Answer: Some genes are very close to Answer: Some genes are very close to each other on the chromosome. each other on the chromosome. Therefore, when one gene is passed down, Therefore, when one gene is passed down, chances are, so will the other one.chances are, so will the other one.