Question 1

Which of the following best describes a null (amorphic) mutation?

Accepted Answer

A mutation that results in no functional protein being produced.

Question 2

Loss-of-function (LOF) mutations most commonly produce which type of phenotype?

Accepted Answer

Recessive

Question 3

In the case of tyrosinase gene mutations in cats, which genotype results in an albino phenotype?

Accepted Answer

tt (homozygous mutant)

Question 4

What is the definition of haploinsufficiency?

Accepted Answer

A condition where half the amount of wild-type gene product is NOT sufficient for a wild-type phenotype.

Question 5

Which equation best represents the total amount of protein produced in a heterozygote for a gene with one wild-type and one null allele?

Accepted Answer

$P_{total} = P_{WT} + P_{null}$

Question 6

A dominant-negative mutation is best described as:

Accepted Answer

A mutation whose gene product interferes with the function of the wild-type protein.

Question 7

In snapdragon flowers, the heterozygote for a pigment enzyme gene shows a pink phenotype. This is an example of:

Accepted Answer

Incomplete dominance

Question 8

Which of the following scenarios is an exception to the rule that most LOF mutations are recessive?

Accepted Answer

Haploinsufficiency

Question 9

If a gene product has a threshold amount required for wild-type phenotype, what happens in a heterozygote with one null allele if the threshold is not met?

Accepted Answer

The phenotype will be mutant due to haploinsufficiency.

Question 10

Which statement is TRUE regarding recessive alleles?

Accepted Answer

Recessive alleles may be transcribed and translated, but do not affect the phenotype in the presence of a wild-type allele.

Question 11

A patient has a mutation in one allele of a gene encoding a multimeric protein, and the mutant subunit disrupts the function of the entire protein complex. This is an example of:

Accepted Answer

Dominant-negative mutation

Question 12

Which genotype would you expect to show a mutant phenotype if the gene exhibits haploinsufficiency?

Accepted Answer

Heterozygous (one wild-type, one mutant allele)

Question 13

If $A_1$ is a wild-type allele and $A_2$ is a mutant allele with a dominant-negative effect, what is the expected phenotype of an $A_1A_2$ heterozygote?

Accepted Answer

Mutant

Question 14

Which of the following best explains why most LOF mutations are recessive?

Accepted Answer

One wild-type allele usually produces enough gene product for a normal phenotype.

Question 15

In a gene with no threshold for protein activity, what is the expected phenotype of a heterozygote with one wild-type and one null allele?

Accepted Answer

Intermediate phenotype

Question 16

Which of the following is NOT a possible outcome of a loss-of-function mutation?

Accepted Answer

Gain of protein function

Question 17

A gene encoding an enzyme for pigment production in flowers has two alleles: $C^R$ (red) and $C^W$ (white, null). What is the phenotype of a $C^RC^W$ heterozygote if there is no threshold for enzyme activity?

Accepted Answer

Pink

Question 18

Which of the following best describes the informative value of the heterozygous state?

Accepted Answer

It allows determination of the relationship between two alleles for a gene of interest.

Question 19

Which of the following is a real-world example of a gene with a dominant-negative mutation?

Accepted Answer

A mutation in collagen genes causing osteogenesis imperfecta.

Genetic Diversity: Effects of Mutations

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