Question 1

Which of the following best describes a monogenic trait?

Accepted Answer

A trait for which alleles of a single gene contribute all of the observed phenotypic variation.

Question 2

In the melanin synthesis pathway, loss-of-function alleles of the tyrosinase gene ($$c) $$cause which phenotype in mammals?

Accepted Answer

Albinism (colorless coat)

Question 3

Which genetic interaction is defined as the masking of the phenotypic effect of one gene by alleles of another gene?

Accepted Answer

Epistasis

Question 4

A dihybrid cross ($$AaBb 	imes AaBb) $$involving recessive epistasis typically produces which modified phenotype ratio in the F2 generation?

Accepted Answer

$$9:3:4$$

Question 5

In Labrador retrievers, which two genes are responsible for coat color variation?

Accepted Answer

E (Mc1R) and B (TYRP1)

Question 6

Which of the following is an example of complementary gene action (mutual recessive epistasis)?

Accepted Answer

Two genes act in the same pathway, and both must have at least one dominant allele for the wild-type phenotype to be produced.

Question 7

Which modified phenotype ratio is expected in the F2 generation of a dihybrid cross showing dominant epistasis?

Accepted Answer

$$12:3:1$$

Question 8

Redundancy (mutual dominant epistasis) is observed when:

Accepted Answer

Multiple genes perform the same function, so only one dominant allele is needed for the wild-type phenotype.

Question 9

Which of the following best describes the role of modifier genes in genetic pathways?

Accepted Answer

Modifier genes alter the phenotypic effect of alleles of a second gene, but do not produce a phenotype on their own.

Question 10

A genetic modifier screen is used to:

Accepted Answer

Identify new genes involved in a pathway based on their ability to modify the phenotype of a gene already known to act in that pathway.

Question 11

In a genetic modifier screen for cancer in Drosophila, researchers identified suppressor genes of a mutant KRAS allele. Why are these suppressor genes important?

Accepted Answer

They can reveal new drug targets and help understand the pathways involved in cancer.

Question 12

Which system allows researchers to generate conditional alleles in Drosophila by using two transgenes?

Accepted Answer

UAS/Gal4 system

Question 13

In the UAS/Gal4 system, what is the function of the Gal4 protein?

Accepted Answer

It binds to the UAS sequence and activates transcription of the downstream gene.

Question 14

Which of the following is NOT a type of genetic pathway discussed in the study materials?

Accepted Answer

Epigenetic pathway

Question 15

If a Labrador retriever has the genotype $$ee$$ for the E gene and $$B-$$ for the B gene, what will its coat color be?

Accepted Answer

Yellow (due to $$ee$$ masking $$B)$$

Question 16

Which equation represents the expected genotype ratio for a dihybrid cross ($$AaBb 	imes AaBb) $$under standard Mendelian inheritance?

Accepted Answer

$$9:3:3:1$$

Question 17

A researcher observes that a loss-of-function allele in gene X only produces a phenotype when gene Y is also mutated. This is an example of:

Accepted Answer

Complementary gene action

Question 18

Which of the following statements about enhancer alleles is correct?

Accepted Answer

Enhancer alleles strengthen the phenotypic effect of a second gene.

Question 19

In a genetic pathway, which type of gene interaction is indicated when the phenotype of one gene is only observable if the other gene is functional?

Accepted Answer

Epistasis

Question 20

Which of the following best explains why geneticists study epistasis?

Accepted Answer

Epistasis indicates that two genes function in the same pathway.

Genetic Pathways and Genetic Interactions: Epistasis, Modifier Genes, and Conditional Alleles

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