Q: Which of the following is the correct formula for calculating the proportion of progeny with a given phenotype in a dihybrid cross?

$$x = \frac{\text{number of progeny with a phenotype}}{16}$$

Question 1

In a classic dihybrid cross (AaBb x AaBb) with independent assortment and complete dominance at both loci, what is the expected phenotypic ratio among the offspring?

Accepted Answer

$$9:3:3:1$$

Question 2

Which of the following best describes epistasis?

Accepted Answer

One gene masks the effect of another gene at a different locus

Question 3

A Labrador retriever with genotype aaBb is crossed with a Labrador retriever with genotype Aabb. What are the possible coat colors of the offspring and their expected ratio?

Accepted Answer

1 brown : 1 golden

Question 4

In the case of recessive epistasis, such as coat color in Labrador retrievers, what is the expected phenotypic ratio in the F2 generation from a dihybrid cross?

Accepted Answer

$$9:3:4$$

Question 5

A dog breeder crosses a yellow Labrador (aaBb) with a brown Labrador (Aabb) and all the puppies are black. What is the most likely explanation for this result?

Accepted Answer

The yellow parent was actually heterozygous at the A locus (AaBb)

Question 6

Which of the following is an example of dominant epistasis?

Accepted Answer

Fruit color in summer squash

Question 7

In the summer squash, the presence of a dominant A allele results in white fruit regardless of the B locus. What is the expected phenotypic ratio in the F2 generation from a dihybrid cross AaBb x AaBb?

Accepted Answer

$$12:3:1$$

Question 8

A person with the Bombay phenotype is homozygous for a recessive mutation at the H locus (hh). What is the effect on their ABO blood type?

Accepted Answer

They will appear as blood type O regardless of their ABO genotype

Question 9

Which of the following best defines an epistatic allele?

Accepted Answer

An allele that masks the effect of alleles at another locus

Question 10

In a dihybrid cross involving two genes with no interaction, what are the assumptions required for the classic $$9:3:3:1$$ phenotypic ratio to be observed?

Accepted Answer

Both loci assort independently, each locus shows complete dominance, and each phenotype is unambiguous

Question 11

A cross between two pink panthers produces offspring in the ratio 12 pink : 3 black : 1 white. What type of gene interaction does this ratio indicate?

Accepted Answer

Dominant epistasis

Question 12

In the context of gene interaction, what is meant by a 'novel phenotype'?

Accepted Answer

A phenotype not seen in either parent, resulting from the interaction of alleles at two loci

Question 13

If a person with genotype Hh and blood type O mates with a person who is also Hh and has AB blood, what blood types are possible among their children?

Accepted Answer

A, B, AB, and O

Question 14

Which of the following is the correct formula for calculating the proportion of progeny with a given phenotype in a dihybrid cross?

Accepted Answer

$$x = \frac{	ext{number of progeny with a phenotype}}{16}$$

Question 15

In the case of dominant epistasis, which genotype(s) in summer squash will result in white fruit?

Accepted Answer

A_B_ and A_bb

Question 16

Which of the following best describes the hypostatic allele?

Accepted Answer

An allele whose effect is masked by an allele at a different locus

Question 17

A dihybrid cross produces a phenotypic ratio of $$9:7. $$What type of gene interaction does this suggest?

Accepted Answer

Duplicate recessive epistasis

Question 18

In the context of Labrador retriever coat color, which gene is epistatic and which is hypostatic?

Accepted Answer

Gene A is epistatic, Gene B is hypostatic

Question 19

If two genes interact such that the presence of a dominant allele at either locus produces the same phenotype, what is the expected F2 phenotypic ratio?

Accepted Answer

$$15:1$$

Question 20

Which of the following scenarios would violate the assumptions required for a $$9:3:3:1$$ dihybrid ratio?

Accepted Answer

The two genes are linked on the same chromosome

Extensions to Mendelian Inheritance: Gene Interaction and Epistasis

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