Chapter 7. 7·6–7·8 Probability and chance play central roles in genetics.

Show What You Know - Self Quiz

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You must read each slide, and complete any questions on the slide, in sequence.

Instructions

Check your understanding of concepts from 7·6– 7·8 Probability and chance play central roles in genetics by answering the following questions.

1.

1. The test-cross:

makes it possible to determine the genotype of an individual of unknown genotype who exhibits the dominant version of a trait.

is a cross of an individual whose genotype for a trait is not known with an individual homozygous dominant for the trait.

requires the self-fertilization of an individual whose genotype is unknown.

A and B are both correct.

A, B, and C are correct.

Correct! (See section 7·7 A test-cross enables us to figure out which alleles an individual carries.)

Incorrect. (See section 7·7 A test-cross enables us to figure out which alleles an individual carries.)

2.

2. Assuming that a particular disorder is caused by an allele of a single gene, what feature of a pedigree would allow one to conclude that the disorder was caused by a dominant allele?

An affected mother only has affected sons.

All of the descendants of a particular affected person are also affected.

There is no way to tell based on pedigree analysis alone.

Two affected parents have an unaffected child.

Two unaffected parents have an affected child.

Correct! (See section 7·8 We use pedigrees to decipher and predict the inheritance patterns of genes.)

Incorrect. (See section 7·8 We use pedigrees to decipher and predict the inheritance patterns of genes.)

3.

3. The chance of two separate events occurring together is equal to the product of their separate chances. Two people who are carriers of the recessive Tay-Sachs gene decide to have children. What are the chances this couple will give birth to three children with Tay-Sachs?

None; they can't produce any Tay-Sachs children.

1/16 or 12.5%

1/64 or 1.56%

1/4 or 25%

1/8 or 50%

Correct! (See section 7·6 Chance is important in genetics.)

Incorrect. (See section 7·6 Chance is important in genetics.)

4.

4. In peas, yellow seeds (Y) are dominant to green seeds (y). A homozygous dominant and a homozygous recessive plant are crossed and have two offspring. These two offspring are now crossed with each other. What are the chances that the second generation of offspring (the offspring of the first offspring) will have yellow seeds?

75%

50%

100%

25%

Correct! (See section 7·6 Chance is important in genetics.)

Incorrect. (See section 7·6 Chance is important in genetics.)

5.

5. In pea plants, the allele for purple flower color is dominant to the allele for white flower color. If you were to perform a test-cross to determine the genotype of a purple-flowered plant, you would expect the percehtage of purple-flowered progeny to be _________ if the plant is homozygous and _____________ if the plant is heterozygous.

100%, 25%

75%, 25%

50%, 100%

75%, 75%

100%, 50%

Correct! (See section 7·7 A test-cross enables us to figure out which alleles an individual carries.)

Incorrect. (See section 7·7 A test-cross enables us to figure out which alleles an individual carries.)

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