Question 1

Which of the following best describes a haplosufficient allele?

Accepted Answer

An allele where one copy is enough to produce the wild-type phenotype.

Question 2

A patient is heterozygous for a null mutation in a gene encoding an enzyme. If the wild-type allele is haplosufficient, what phenotype would you expect?

Accepted Answer

Wild-type phenotype, because one functional allele produces enough enzyme.

Question 3

Which of the following is an example of codominance?

Accepted Answer

ABO blood group where both $$I^A$$ and $$I^B$$ alleles are expressed in the phenotype.

Question 4

A cross between two yellow mice (genotype $$A^Y A) $$produces a 2:1 ratio of yellow to agouti offspring. What is the most likely explanation?

Accepted Answer

The $$A^Y$$ allele is lethal in the homozygous state ($$A^Y A^Y).$$

Question 5

Which of the following best describes a leaky (hypomorphic) mutation?

Accepted Answer

A mutation that reduces but does not eliminate gene product function.

Question 6

In the context of gene interactions, what is epistasis?

Accepted Answer

When an allele of one gene masks or modifies the expression of alleles at another gene.

Question 7

A plant with genotype $$Rr$$ produces 50 units of enzyme, while $$RR$$ produces 100 units and $$rr$$ produces 0 units. If 40 units are required for the wild-type phenotype, what is the dominance relationship?

Accepted Answer

The $$R$$ allele is haplosufficient and dominant to $$r.$$

Question 8

Which of the following is an example of a pleiotropic gene?

Accepted Answer

A gene that affects both flower color and seed coat color in peas.

Question 9

A genetic disorder is caused by a dominant allele, but only 70% of individuals with the allele show symptoms. What is this phenomenon called?

Accepted Answer

Incomplete penetrance

Question 10

Which of the following best describes the one gene-one enzyme hypothesis?

Accepted Answer

Each gene encodes a single enzyme that affects a specific step in a metabolic pathway.

Question 11

A woman with type AB blood and a man with type O blood have a child. What are the possible blood types for their child?

Accepted Answer

Type A or Type B

Question 12

Which of the following is a real-world example of a gene-environment interaction?

Accepted Answer

Phenylketonuria (PKU) symptoms can be prevented by dietary restriction of phenylalanine.

Question 13

In a population, a gene has five different alleles. How many alleles can a single diploid individual carry for this gene?

Accepted Answer

2

Question 14

Which of the following best describes variable expressivity?

Accepted Answer

Individuals with the same genotype show different degrees of the phenotype.

Question 15

A cross between two pure-breeding plants, one with red flowers and one with white flowers, produces all pink-flowered offspring. What type of inheritance is this?

Accepted Answer

Incomplete dominance

Question 16

Which of the following is true about dominant negative mutations?

Accepted Answer

They produce gene products that interfere with the function of the wild-type allele.

Question 17

In a dihybrid cross with no epistasis, what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$$9:3:3:1$$

Question 18

Which of the following is an example of a sex-influenced trait?

Accepted Answer

Beard development in goats, where the same genotype produces different phenotypes in males and females.

Question 19

A researcher crosses two white-flowered plants from different populations and all F1 offspring have purple flowers. What does this indicate?

Accepted Answer

The mutations are in different genes (complementation).

Question 20

Which of the following best describes a neomorphic mutation?

Accepted Answer

A mutation that results in a novel gene product activity not found in the wild type.

Gene Interactions: Mechanisms and Phenotypic Outcomes

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