DO NOW:

Can you roll your tongue? Do you have a widow’s peak? Are your earlobes attached or do they dangle?

Objectives:

1.Explain the relationship between traits and heredity.2.Describe the experiments of Gregor Mendel.3.Differentiate between dominant and recessive traits.

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Gregor Mendel was born in 1822 in

Heinzendorf, Austria.

At age 21, Mendel entered a monastery. Performed many scientific experiments in the

monastery garden.

Mendel discovered the principles of heredity, the passing of traits from parents to offspring.

Who was Gregor Mendel?

Mendel used garden pea plants for his

experiments. Self-Pollinating Peas have both male and female

reproductive structures. So, pollen from one flower can fertilize the ovule of the same flower.

Pea plants also grow quickly, allowing him to produce many generations within a short time span.

When a true-breeding plant self pollinates, all of the offspring will have the same trait as the parent.

Unraveling the Mystery

Pea plants can also

cross-pollinate. Pollen from one plant

fertilizes the ovule of a flower on a different plant.

The image shows cross-pollination and self-pollination.

Unraveling the Mystery

Characteristics

Mendel studied only one pea characteristic at a time.

A characteristic is a feature that has different forms in a population. (Ex. Eye color)

Different forms of a characteristic are called traits. (Ex. Brown and Blue)

Unraveling the Mystery, continued

Mix and Match

Mendel was careful to use plants that were true breeding for each of the traits he was studying.

This allowed him to know what to expect if his plants were to self-pollinate.

Unraveling the Mystery, continued

Mendel crossed pea plants to study seven different

characteristics.

He noticed that one trait was always present in the first generation, and the other trait seemed to disappear.

Mendel called the trait that appeared the dominant trait.

The trait that seemed to fade into the background was

called the recessive trait.

Mendel’s First Experiments

To find out more about

recessive traits, Mendel allowed the first-generation plants to self-pollinate.

In each case some of the second-generation plants had the recessive trait.

Mendel’s Second Experiments

Ratios in Mendel’s

Experiments The recessive trait did not

show up as often as the dominant trait.

Mendel decided to figure out the ratio of dominant traits to recessive traits.

Mendel’s Second Experiments, continued

In all cases

the ratio was about 3:1 dominant : recessive.

Mendel’s Second Experiments, continued

Gregor Mendel – Gone But Not Forgotten

Mendel realized that his results could be explained only if each plant had two sets of instructions for each characteristic.

Mendel’s work opened the door to modern genetics.

Mendel’s Second Experiments, continued

DO NOW:

Why did Mendel decide to use pea plants to further his understanding of heredity?

Objectives:

1.Explain the relationship between traits and heredity.2.Describe the experiments of Gregor Mendel.3.Differentiate between dominant and recessive traits.

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