Question 1

A wild-type allele (R+) produces 50 units of enzyme activity, while a mutant allele (r) produces 0 units. If 40 or more units are required for a wild-type phenotype, which of the following best describes the dominance relationship and the concept illustrated?

Accepted Answer

The wild-type allele is haplosufficient and dominant to the mutant allele.

Question 2

A patient with phenylketonuria (PKU) is able to live a normal life if their diet is strictly controlled to avoid phenylalanine. What genetic principle does this scenario best illustrate?

Accepted Answer

Gene–environment interaction

Question 3

Which of the following best describes a dominant negative mutation?

Accepted Answer

A mutation in a multimeric protein that disrupts the function of the entire protein complex, even in the presence of a wild-type allele.

Question 4

In the ABO blood group system, which genotype results in the expression of both A and B antigens on the surface of red blood cells?

Accepted Answer

$$I^A I^B$$

Question 5

A cross between two pea plants with genotypes $$T_1T_2 ($$incomplete dominance for flowering time) results in offspring with three distinct flowering times. Which of the following best explains this observation?

Accepted Answer

Incomplete dominance, where the heterozygote has an intermediate phenotype.

Question 6

A mutation in the C gene of rabbits produces a temperature-sensitive enzyme, resulting in dark fur on the extremities and white fur on the body. What type of mutation is this?

Accepted Answer

Hypomorphic (temperature-sensitive) mutation

Question 7

Which of the following best describes pleiotropy?

Accepted Answer

A single gene mutation affects multiple distinct traits.

Question 8

A woman with polydactyly (extra fingers), an autosomal dominant trait, has a child with the same genotype but only five fingers. What genetic concept does this illustrate?

Accepted Answer

Incomplete penetrance

Question 9

In a population of goats, the B1 allele is beardless and the B2 allele is bearded. B1B2 males are bearded, but B1B2 females are beardless. What is this an example of?

Accepted Answer

Sex-influenced trait

Question 10

Which of the following equations correctly represents the expected phenotypic ratio for a dihybrid cross with complete dominance and independent assortment?

Accepted Answer

$$9:3:3:1$$

Question 11

A gene has three alleles: $$A_1$$, $$A_2$$, and $$A_3$$. $$A_1 is $$dominant to both $$A_2$$ and $$A_3$$, and $$A_2 is $$dominant to $$A_3. $$What is this hierarchy called?

Accepted Answer

Allelic series

Question 12

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

Accepted Answer

A mutation that produces a reduced amount of functional gene product.

Question 13

A trait is only expressed in males, even though both sexes carry the gene. What is this trait called?

Accepted Answer

Sex-limited trait

Question 14

Which of the following is an example of a gain-of-function mutation?

Accepted Answer

A mutation that causes a gene product to be active in a new tissue where it is not normally expressed.

Question 15

Which of the following best describes codominance?

Accepted Answer

Both alleles are fully expressed in the heterozygote, resulting in a phenotype distinct from either homozygote.

Question 16

A person with Waardenburg syndrome may have different combinations of symptoms, even though all affected family members have the same genotype. What genetic concept does this illustrate?

Accepted Answer

Variable expressivity

Question 17

Which of the following best describes epistasis?

Accepted Answer

The interaction of two or more genes to control a single phenotype, often modifying Mendelian ratios.

Question 18

In the context of gene interaction, what is the main difference between anabolic and catabolic pathways?

Accepted Answer

Anabolic pathways build complex molecules, while catabolic pathways break them down.

Question 19

A mutation in the β-globin gene causes sickle cell disease, which leads to anemia, pain, and organ damage. What genetic principle does this illustrate?

Accepted Answer

Pleiotropy

Question 20

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

Accepted Answer

A mutation that produces no functional gene product.

Gene Interaction and Extensions to Mendelian Inheritance

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