How are traits passed from parents to offspring?

Mendel and His Peas

• Why did Mendel perform cross-pollination experiments?

• What did Mendel conclude about inherited traits?

• How do dominant and recessive factors interact?

• heredity

• genetics

• dominant trait

• recessive trait

Mendel and His Peas

• Heredity is the passing of traits from parents to offspring.

• Gregor Mendel is known as the father of genetics—the study of how traits are passed from parents to offspring.

Early Ideas About Heredity

• Mendel studied genetics by doing controlled breeding experiments with pea plants.

• There are two types of pollination:

• self-pollination

• cross-pollination

Mendel’s Experimental Methods

Self-Pollination

• When a true-breeding plant self-pollinates, it always produces offspring with traits that match the parent.

• Mendel cross-pollinated pea plants himself and recorded the traits that appeared.

Mendel’s Experimental Methods (cont.)

Cross-Pollination

Mendel’s Experimental Methods (cont.)

Why did Mendel perform cross-pollination experiments?

• Once Mendel had enough true-breeding plants for a trait he wanted to test, he cross-pollinated selected plants.

• Plants are called hybrids if they come from true-breeding parent plants with different forms of the same trait.

Mendel’s Results

First-Generation Crosses

hybrid

Science Use the offspring of two animals or plants with different forms of the same trait

Common Use having two types of components that perform the same function, such as a vehicle powered by both a gas engine and an electric motor

Mendel’s Results (cont.)

• Mendel also cross-pollinated hybrid plants.

• He observed that offspring of hybrid crosses always showed traits in a 3:1 ratio.

Mendel’s Results (cont.)

Second-Generation (Hybrid) Crosses

Mendel’s Results (cont.)

Mendel recorded traits of offspring from many hybrid crosses.

Mendel concluded that two factors, one from each sperm and one from each egg, control each inherited trait.

Mendel’s Conclusions

What did Mendel conclude about inherited traits?

Mendel’s Conclusions (cont.)

• A dominant trait is a genetic factor that blocks another genetic factor.

• A recessive trait is a genetic factor that is blocked by the presence of a dominant factor.

How do dominant and recessive factors interact?

Mendel’s Conclusions (cont.)

• Genetics is the study of how traits are passed from parents to offspring.

• Mendel studied genetics by doing cross-breeding experiments with pea plants.

• Mendel’s experiments with pea plants showed that some traits are dominant and others are recessive.

A. true breeding

B. self-pollination

C. cross-pollination

D. bees

What method did Mendel use to select which plants pollinated other plants?

A. 0

B. 1

C. 2

D. 1 or 2

How many dominant factors does a purple-flowering pea plant have?

A. 1 : 1

B. 2 : 1

C. 3 : 1

D. 4 : 1

What is the approximate ratio of dominant to recessive expression when both parents are hybrid?

1. Like mixing paints, parents’ traits always blend in their offspring.

2. If you look more like your mother than you look like your father, then you received more traits from your mother.

Do you agree or disagree?