Name Date Class

Assess Your Understanding

What Is Heredity?What Did Mendel Observe?

1a. DEFINE What happens during fertilization?

b. COMPARE AND CONTRAST In Mendel's cross for stem height, how

did the plants in the F2 generations differ from the F, plants?

gotit?O I get it! Now I know that Mendel found that one form of a trait

O I need extra help with

How Do Alleles Affect Inheritance?

2a. relate CAUSE AND EFFECT Why is a pea plant that is a hybrid for stem

height tall?

b. (CHALLENGE Can a short pea plant be a hybrid for the trait of stem

height? Why or why not?

gotit?O I get it! Now I know that an organism's traits are controlled by

O I need extra help with

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79B

Name Date Class

Enrich

What Is Heredity?When an organism has a trait controlled by a dominant allele, it can either be a hybridor a purebred. To find out which, geneticists use a test cross. Read the passage and studythe diagram below. Then use a separate sheet of paper to answer the questions thatfollow the diagram.

The Test CrossIn a test cross, the organism with the trait controlled by a dominant allele is crossed with an organismwith a trait controlled by a recessive allele. If all offspring have the trait controlled by the dominant allele,then the parent is probably a purebred. If any offspring has the recessive strait, then the dominant parentis a hybrid.

Test Cross

P GenerationW - ^ u ^ W ^ - M , ' ^ ^ .

H_?

X

IFt Generation

H

H

H = Short hairh = Long hair

1. Is the long-haired cat in the P generation a hybrid or a purebred?Explain your answer.

2. Is the short-haired cat in the P generation a hybrid or a purebred?Explain your answer.

3. If the short-haired cat in the P generation were purebred, whatwould you expect the offspring to look like?

4. In horses, the allele for a black coat (B) is dominant over the allele fora brown coat Ob). A cross between a black horse and a brown horseproduces a brown foal. Is the black horse a hybrid or a purebred?Explain.

5. In guinea pigs, the allele for a smooth coat (5) is dominant over theallele for a rough coat (s). Explain how you could find out whether aguinea pig with a smooth coat is a hybrid or a purebred.

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Name Date Class

Review and Reinforce

What is Heredity?Understanding Main IdeasStudy the diagram below. Then use a separate sheet of paper to answer the questionsbelow the diagram.

P Generation F1 Generation F2 Generationr ~ r

M f X ^

1. What trait in pea plants is being studied in the cross shown above?

2. What are the two alleles for this trait?

3. Which allele is the dominant allele? Explain how you know.

4. Which allele is the recessive allele? Explain how you know.

5. What alleles do the F, offspring have? Explain which allele wasinherited from each parent.

Building VocabularyMatch each term with its definition by writing the letter of the correct definition in theright column on the line beside the term in the left column.

6. genetics

7. allele

8. trait

9. dominant allele

10. gene

11. hybrid

12. heredity

13. recessive allele

a. the passing of traits from parents to offspring

b. an organism with two different alleles for a trait

c. a factor that controls traits

d. a physical characteristics of organisms

e. an allele whose trait always shows up in the organism

f. each different form of a gene

g. the scientific study of heredity

h. an allele whose trait is hidden in the presence of adominant allele

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79D

Name Date Class

Lesson Quiz

What Is Heredity?If the statement is true, write true. If the statement is false, change the underlined wordor words to make the statement true.

1.

2.

3.

4.

5.

The scientific study of heredity is called fertilization.

A hybrid organism is the offspring of many generations thathave the same form of a trait.

Capital letters are used to represent recessive alleles.

Mendel called an individual that has one dominant allele andone recessive allele for a trait a purebred.

Mendel said that the factors that control a trait exist in pairs.

6. lendel's experiments showed that the traits of an offspringwere not a blend of the characteristics of the parents.

Write the letter of the correct answer on the line at the left.

7. What Mendel called factors are nowcalledA heredityB genesC purebredsD traits

8. When parent plants are crossed,scientists refer to the first generation ofoffspring asA P

B F2C 1FD F,

9. A seed can be round or wrinkled.Seed shape isA a traitB an allele

C a factorD a gene

10. The allele for a hybrid tall pea plant isrepresented asA 7 7B Tt

C T5D t t

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79F