1. Chapter 5
Section 1 Mendel and His Peas
Bellringer
You have probably noticed that different people have different characteristics, such as eye color, hair color, and ear lobes that do or do not attach directly to their head. Where do you think people get these different traits?

2. Chapter 5
Section 1 Mendel and His Peas
Objectives
Explain the relationship between traits and heredity.
Describe the experiments of Gregor Mendel.
Explain the difference between dominant and recessive traits.

3. Chapter 5 Who Was Gregor Mendel?
Section 1 Mendel and His Peas
Who Was Gregor Mendel?
Gregor Mendel was born in 1822 in Heinzendorf, Austria.
At age 21, Mendel entered a monastery. He performed many scientific experi- ments in the monastery garden.
Mendel discovered the principles of heredity, the passing of traits from parents to offspring.

4. Unraveling the Mystery
Chapter 5
Section 1 Mendel and His Peas
Unraveling the Mystery
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.
When a true-breeding plant self pollinates, all of the offspring will have the same trait as the parent.

5. Unraveling the Mystery
Chapter 5
Section 1 Mendel and His Peas
Unraveling the Mystery
Pea plants can also cross-pollinate. Pollen from one plant fertilizes the ovule of a flower on a different plant.

6. Unraveling the Mystery
Chapter 5
Section 1 Mendel and His Peas
Unraveling the Mystery
Mendel studied only one pea characteristic at a time. A characteristic is a feature that has different forms in a population.
Different forms of a characteristic are called traits.

7. Unraveling the Mystery
Chapter 5
Section 1 Mendel and His Peas
Unraveling the Mystery
Mendel was careful to use plants that were true breeding for each of the traits he was studying. By doing so, he would know what to expect if his plants were to self-pollinate.

8. Mendel’s First Experiments
Chapter 5
Section 1 Mendel and His Peas
Mendel’s First Experiments
Mendel crossed pea plants to study seven different characteristics.
Mendel got similar results for each cross. 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.

9. Chapter 5 Mendel’s Second Experiments
Section 1 Mendel and His Peas
Mendel’s Second
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 plats had the recessive trait.

10. Mendel’s Second Experiments
Chapter 5
Section 1 Mendel and His Peas
Mendel’s Second 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.

11. Mendel’s Second Experiments
Chapter 5
Section 1 Mendel and His Peas
Mendel’s Second Experiments
In all cases the ratio was about 3:1 dominant : recessive.

12. Mendel’s Second Experiments
Chapter 5
Section 1 Mendel and His Peas
Mendel’s Second Experiments
Mendel realized that his results could be explained only if each plant had two sets of instructions for each characteristic. He published his findings in 1865.
Mendel’s work opened the door to modern genetics.

13. Chapter 5 Section Summary
Section 1 Mendel and His Peas
Section Summary
Heredity is the passing of traits from parents to offspring.
Gregor Mendel made carefully planned experiments using pea plants that could self-pollinate.
When parents with different traits are bred, dominant traits are always present in the first generation. Recessive traits are not visible in the first generation but reappear in the second generation.
Mendel found a 3:1 ratio of dominant-to-recessive traits in the second generation.