Question 1

Which of the following best describes epistasis?

Accepted Answer

A situation where one pair of alleles can mask the phenotypic effects of another pair of alleles at a different locus.

Question 2

In a dihybrid cross involving two genes that show recessive epistasis, what phenotypic ratio would you expect in the F2 generation?

Accepted Answer

$9:3:4$

Question 3

In the context of epistasis, what is the difference between an epistatic gene and a hypostatic gene?

Accepted Answer

The epistatic gene masks the effect of the hypostatic gene.

Question 4

A mouse with genotype $aaBB$ is crossed with a mouse with genotype $AAbb$. If black pigment requires at least one dominant $B$ allele and agouti pattern requires at least one dominant $A$ allele, what is the expected phenotype of their offspring?

Accepted Answer

All offspring will be agouti.

Question 5

In Labrador retrievers, the $E$ gene is epistatic to the $B$ gene. If a dog is $ee$ at the $E$ locus, what will its coat color be regardless of its $B$ genotype?

Accepted Answer

Yellow

Question 6

Which of the following is an example of dominant epistasis?

Accepted Answer

The $W$ allele in summer squash masking pigment production regardless of the $Y$ gene.

Question 7

In a cross between two heterozygous summer squash plants ($WwYy$), where $W$ is dominant epistatic to $Y$, what is the expected phenotypic ratio for white:yellow:green squash in the F2 generation?

Accepted Answer

$12:3:1$

Question 8

A woman with the Bombay phenotype ($hh$) has blood type O, even though her genotype at the ABO locus is $IAIB$. What genetic principle explains this observation?

Accepted Answer

Recessive epistasis

Question 9

Which of the following crosses would produce a 9:7 phenotypic ratio in the F2 generation, and what does this ratio indicate?

Accepted Answer

A cross involving two genes where both dominant alleles are required for the phenotype (complementary gene interaction).

Question 10

If a plant with genotype $AAbb$ (white flowers) is crossed with a plant with genotype $aaBB$ (white flowers), and all F1 offspring have purple flowers, which genetic phenomenon is most likely responsible?

Accepted Answer

Complementary gene interaction

Question 11

In a dihybrid cross involving two genes with dominant epistasis, what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$12:3:1$

Question 12

Which of the following best explains why the phenotypic ratios in epistatic interactions are often in sixteenths (16ths) rather than fourths (4ths)?

Accepted Answer

Because dihybrid crosses involve two genes, each with two alleles, resulting in $4 	imes 4 = 16$ possible genotypes.

Question 13

A geneticist observes a 9:3:4 phenotypic ratio in the F2 generation of a dihybrid cross. Which of the following is the most likely explanation?

Accepted Answer

Recessive epistasis

Question 14

In the context of epistasis, which of the following statements is correct?

Accepted Answer

Epistasis can modify the expected Mendelian phenotypic ratios in dihybrid crosses.

Question 15

A researcher crosses two plants with genotypes $AaBb$ and $AaBb$. If gene A is epistatic to gene B and the epistasis is recessive, which genotype will result in the masked phenotype?

Accepted Answer

$aabb$

Question 16

Which of the following scenarios is an example of complementary gene interaction?

Accepted Answer

Two genes are required for pigment production, and the absence of a dominant allele at either locus results in white flowers.

Question 17

In a dihybrid cross, which of the following phenotypic ratios would suggest the presence of novel phenotypes due to gene interaction?

Accepted Answer

$9:6:1$

Question 18

A geneticist is studying fruit shape in summer squash. The F2 generation from a cross between disc-shaped ($AABB$) and long-shaped ($aabb$) parents yields a 9:6:1 ratio of disc:oval:long fruit. What does this ratio indicate?

Accepted Answer

Novel phenotypes due to gene interaction

Epistasis: Genetic Interactions and Modified Mendelian Ratios

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