Q: Which of the following crosses would produce a 9:3:4 phenotypic ratio due to epistasis?

$$BbEe \times BbEe$$ where one gene masks the effect of the other.

Question 1

Which of the following best describes epistasis?

Accepted Answer

The expression of one gene masking or modifying the expression of another gene, altering Mendelian ratios.

Question 2

In a dihybrid cross of $$BbEe 	imes BbEe$$ for Labrador coat color, what is the expected phenotypic ratio for black, brown, and yellow dogs?

Accepted Answer

$$9:3:4$$

Question 3

A Labrador retriever with genotype $$bbEe$$ will have which coat color?

Accepted Answer

Brown

Question 4

If a Labrador retriever has the genotype $$Bbee$$, what will its coat color be and why?

Accepted Answer

Yellow, because the ee genotype prevents pigment deposition regardless of the B gene.

Question 5

Which of the following crosses would produce a 9:3:4 phenotypic ratio due to epistasis?

Accepted Answer

$$BbEe 	imes BbEe$$ where one gene masks the effect of the other.

Question 6

In corn, both dominant alleles $$A$$ and $$B$$ are required for purple kernels. What is the expected phenotypic ratio for purple to white kernels in the $$F_2$$ generation of $$AaBb 	imes AaBb$$?

Accepted Answer

$$9:7$$

Question 7

Which scenario best illustrates polygenic inheritance?

Accepted Answer

Multiple genes contribute to the continuous variation in human eye color.

Question 8

A plant species has three genes (A, B, C) controlling kernel color, with dominant alleles producing red pigment. What is the minimum number of dominant alleles required for a kernel to be red?

Accepted Answer

At least one dominant allele at each gene (A, B, and C).

Question 9

Which of the following best explains why Himalayan rabbits have darker fur on their extremities?

Accepted Answer

The pigment-producing enzyme is active at lower temperatures found in the extremities.

Question 10

Hydrangea flower color is influenced by soil pH due to the availability of aluminum ions. What color will hydrangeas likely be in acidic soil?

Accepted Answer

Blue

Question 11

Which of the following is a key difference between polygenic traits and traits showing epistasis?

Accepted Answer

Polygenic traits are influenced by multiple genes, often resulting in continuous variation, while epistasis involves one gene masking the effect of another, altering discrete phenotypic ratios.

Question 12

A cross between two $$BbEe$$ Labradors produces offspring. What fraction of the offspring will be yellow regardless of their B gene genotype?

Accepted Answer

$$1/4$$

Question 13

Which of the following best describes the effect of environment on phenotype?

Accepted Answer

Environment can modify the expression of genetic traits, as seen in Himalayan rabbits and hydrangeas.

Question 14

If a trait shows continuous variation and is quantifiable, which genetic mechanism is most likely responsible?

Accepted Answer

Polygenic inheritance

Question 15

Which genotype combination in corn will NOT produce purple kernels if both $$A$$ and $$B$$ are required for purple pigment?

Accepted Answer

$$AAbb$$

Question 16

A student claims that all traits showing a 9:3:3:1 ratio in the $$F_2$$ generation are not affected by epistasis. Is this claim correct?

Accepted Answer

No, because epistasis can alter the expected Mendelian ratios.

Question 17

Which of the following is an example of a trait influenced by both genetics and environment?

Accepted Answer

Hydrangea flower color, which depends on both genotype and soil pH.

Question 18

If a trait is controlled by three genes, each with two alleles, how many possible genotypes are there for this trait?

Accepted Answer

$$2^6 = 64$

Question 19

Which of the following best explains why some traits do not fit into clearly distinct categories but instead show a range of phenotypes?

Accepted Answer

They are controlled by multiple genes and influenced by environmental factors.

Epistasis, Polygenic Traits, and Environmental Effects on Phenotype

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