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Directed Reading Section: Complex Patterns of Heredity In the space provided, explain how the terms in each pair differ in meaning.

1. polygenic trait, multiple alleles

2. incomplete dominance, codominance

Complete each statement by writing the correct term or phrase in the space provided.

3. Sometimes genes are damaged or are copied incorrectly, resulting in faulty

. 4.

is a genetic disorder caused by a defective gene that makes a protein necessary to pump chloride in and out of cells.

Read each question, and write your answer in the space provided.

5. Who should go for genetic counseling prior to having children?

6. What is gene therapy?

Copyright © by Holt, Rinehart and Winston. All rights reserved.

Holt Biology

7

Mendel and Heredity

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Answer Key Directed Reading

have a parent with the trait. If a trait is recessive, an individual with the trait may have one, two, or no parents with the trait.

SECTION: THE ORIGINS OF GENETICS 1. Knight discovered that the purple-

2.

3.

4. 5. 6. 7.

SECTION: COMPLEX PATTERNS OF HEREDITY

flowered offspring of a cross between garden peas with purple flowers and garden peas with white flowers produce some offspring with purple flowers and some with white flowers. Mendel carefully counted the number of each kind of offspring, analyzed the data, and discovered that the numbers formed simple ratios. Garden peas have many traits with two clearly different forms; it is easy to control matings in garden peas; and garden peas are small, mature quickly, and produce numerous offspring. monohybrid P F1 F2

1. A polygenic trait is a trait that is influ-

2.

3. 4. 5. 6.

SECTION: MENDEL’S THEORY 1. 2. 3. 4. 5. 11.

f 6. e a 7. d g 8. y b 9. tall c 10. short The law of segregation states that the two alleles for a trait segregate when gametes are formed during meiosis. 12. The law of independent assortment states that the pairs of alleles for different traits separate independently of one another during meiosis.

enced by several genes. A trait determined by multiple alleles is controlled by a gene that has three or more alleles. Incomplete dominance occurs when offspring display a form of a trait that is intermediate between the forms of the trait displayed by the parents. Codominance occurs when two alleles for a characteristic are expressed at the same time. proteins cystic fibrosis people with a family history of genetic disorders Gene therapy is a procedure that attempts to replace defective genes by inserting copies of healthy genes into an individual.

Active Reading SECTION: THE ORIGINS OF GENETICS 1. A monohybrid cross involves only one 2. 3. 4.

SECTION: STUDYING HEREDITY 1. recessive 2. homozygous 3. heterozygous 1 4. 2

5. 6. 7. 8. 9. 10. 11.

5. 0 1 6. 2 7. If a trait is autosomal, it will appear

equally in both sexes. 8. If an autosomal trait is dominant, every individual with the trait will

pair of contrasting traits. It provides a specific example of a monohybrid cross. This plant would produce only plants with white flowers. The parental generation is the first two individuals that are crossed in a breeding experiment. the first filial generation or first offspring of the parental generation P F1 F2 cross-pollination self-pollination c

Copyright © by Holt, Rinehart and Winston. All rights reserved.

Holt Biology

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Mendel and Heredity