Question 1

Which statement best describes a haplosufficient allele?

Accepted Answer

An allele for which a single copy is sufficient to generate the wild type phenotype.

Question 2

In the context of incomplete dominance, what is the expected phenotypic ratio in the F2 generation from a cross between two heterozygotes ($$R^1R^2$ 	imes R^1$R^2$$)?

Accepted Answer

$$1:2:1 ($$red:pink:white)

Question 3

Which of the following best describes codominance?

Accepted Answer

Both alleles are fully expressed in the heterozygote, resulting in a phenotype that shows both traits distinctly.

Question 4

A person with genotype $$I^A I^B$$ for the ABO blood group will have which phenotype?

Accepted Answer

Type AB

Question 5

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

Accepted Answer

A mutation that results in no functional protein being produced.

Question 6

If a genotype shows a specific phenotype 80% of the time, what is the penetrance?

Accepted Answer

80%

Question 7

Variable expressivity refers to:

Accepted Answer

The range of signs and symptoms that can occur in different people with the same genetic condition.

Question 8

Which genetic phenomenon is illustrated by the Bombay phenotype in human blood groups?

Accepted Answer

Recessive epistasis

Question 9

In a pedigree, if some individuals with the genotype for polydactyly do not show extra digits, this is an example of:

Accepted Answer

Incomplete penetrance

Question 10

Which of the following ratios suggests that epistasis is occurring in a dihybrid cross?

Accepted Answer

$$3:6:3:4$$

Question 11

A cross between two snapdragons with pink flowers ($$R^1R^2$) produces offspring with red, pink, and white flowers. What is the genotype of the white-flowered offspring?

Accepted Answer

$$R^2R^2$

Question 12

Which statement about haploinsufficient alleles is correct?

Accepted Answer

A single copy of the allele is not enough to produce the wild type phenotype.

Question 13

In the ABO blood group system, which genotype(s) will result in type O blood?

Accepted Answer

$$i i$$

Question 14

Which of the following best explains the difference between incomplete dominance and codominance?

Accepted Answer

Incomplete dominance results in a blended phenotype, while codominance results in both traits being fully expressed.

Question 15

A child is born with type O blood, but both parents are type AB. Which genetic phenomenon could explain this?

Accepted Answer

Recessive epistasis (Bombay phenotype)

Question 16

If a gene shows variable expressivity, what would you expect to see in a population?

Accepted Answer

Individuals with the genotype show a range of phenotypes of varying intensity.

Question 17

Which of the following is true about Mendel’s law of segregation?

Accepted Answer

It states that alleles segregate independently and one is dominant over the other.

Question 18

In a dihybrid cross involving recessive epistasis, what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$$9:3:4$$

Question 19

Which of the following scenarios best illustrates gene interaction (epistasis)?

Accepted Answer

One gene masks or modifies the effect of another gene on a single phenotype.

Question 20

A pedigree shows that not all individuals with the genotype for a genetic disorder express the disorder. What is this an example of?

Accepted Answer

Incomplete penetrance

Gene Interactions: Dominance, Penetrance, Expressivity, and Epistasis CH 4

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