Question 1

Which of the following best describes a null mutation in a protein-coding gene?

Accepted Answer

A mutation that produces a non-functional protein product.

Question 2

A Drosophila mutant has eyes that are present but much smaller than wild type. Which type of mutation is most likely responsible for this phenotype?

Accepted Answer

Leaky mutation

Question 3

In a haploinsufficient system, which genotype would most likely display a mutant phenotype if the wild-type allele produces 50 units of enzyme, the mutant allele produces 5 units, and 70 units are required for normal function?

Accepted Answer

$$A^+/A^-$$

Question 4

Which of the following best explains why some mutant alleles act as dominant rather than recessive?

Accepted Answer

They can interfere with the function of the wild-type allele, such as in dominant negative mutations.

Question 5

A cross between two heterozygous four-o’clock plants ($$R/W 	imes R/W) $$produces offspring with red, pink, and white flowers. What is the expected phenotypic ratio?

Accepted Answer

$$1:2:1 ($$red:pink:white)

Question 6

Which genotype results in blood type AB in humans, demonstrating co-dominance?

Accepted Answer

$$I^A/I^B$$

Question 7

In a mouse cross where yellow coat color is dominant but homozygous yellow ($$Y/Y) is $$lethal, what is the expected phenotypic ratio among surviving offspring from $$Y/y 	imes Y/y$$?

Accepted Answer

$$2:1 ($$yellow:nonyellow)

Question 8

Which of the following best defines penetrance?

Accepted Answer

The percentage of individuals with a given genotype who express the expected phenotype.

Question 9

Beadle and Tatum’s experiments with Neurospora mutants demonstrated which principle?

Accepted Answer

One gene is responsible for one polypeptide.

Question 10

A complementation test is performed between two Drosophila mutants with similar wing defects. The F1 offspring all have wild-type wings. What does this indicate?

Accepted Answer

The mutations are in different genes.

Question 11

In a dihybrid cross ($$A/a\ B/b 	imes A/a\ B/b$$), which F2 phenotypic ratio suggests complementary gene interaction?

Accepted Answer

$$9:7$$

Question 12

Which of the following is an example of recessive epistasis?

Accepted Answer

A $$9:3:4$$ phenotypic ratio in the F2 generation.

Question 13

In the context of gene interactions, what does a $$12:3:1$$ ratio in the F2 generation indicate?

Accepted Answer

Dominant epistasis

Question 14

A geneticist observes that a mutation in gene A prevents the expression of gene B’s phenotype, regardless of gene B’s genotype. What is this an example of?

Accepted Answer

Epistasis

Question 15

If a metabolic pathway requires both gene A and gene B to function, and a mutation in either gene results in the same mutant phenotype, what F2 ratio would you expect from a dihybrid cross?

Accepted Answer

$$9:7$$

Question 16

Which of the following best describes variable expressivity?

Accepted Answer

Individuals with the same genotype express the phenotype to varying degrees.

Question 17

A patient with sickle-cell anemia has the genotype $$Hb^S/Hb^S. $$This is an example of which type of allele?

Accepted Answer

Recessive lethal

Question 18

Which of the following scenarios is an example of a dominant negative mutation?

Accepted Answer

A mutant protein interferes with the function of the wild-type protein in a complex.

Question 19

In a complementation test, two mutants are crossed and the F1 offspring all display the mutant phenotype. What does this indicate?

Accepted Answer

The mutations are in the same gene.

Question 20

A gene has two alleles: $$A^+ ($$wildtype, 50 units of enzyme) and $$A^- ($$mutant, 5 units). If the threshold for normal function is 25 units, what is the phenotype of an $$A^+/A^-$$ individual?

Accepted Answer

Wild-type phenotype due to haplosufficiency

Gene Interactions: Patterns, Mechanisms, and Genetic Analysis

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