Question 1

Which of the following best describes a null allele?

Accepted Answer

An allele that produces a nonfunctional gene product due to a loss-of-function mutation.

Question 2

In snapdragons, crossing a red-flowered plant with a white-flowered plant produces pink-flowered offspring. What type of inheritance does this illustrate?

Accepted Answer

Incomplete (partial) dominance

Question 3

A man with blood type AB and a woman with blood type O have children. Which blood types are possible among their offspring?

Accepted Answer

A and B only

Question 4

Which equation correctly represents the expected phenotypic ratio for a dihybrid cross with recessive epistasis?

Accepted Answer

$$9:3:4$$

Question 5

In the ABO blood group system, which statement is correct regarding the alleles?

Accepted Answer

Alleles IA and IB are codominant, and both are dominant to i.

Question 6

A cross between two yellow mice (genotype $$A^Y A) $$results in a 2:1 ratio of yellow to agouti offspring. What explains the absence of $$A^Y A^Y$$ individuals?

Accepted Answer

The $$A^Y$$ allele is a recessive lethal allele.

Question 7

Which scenario best illustrates codominance?

Accepted Answer

Both alleles in a heterozygote are fully expressed, as in MN blood group.

Question 8

A woman with the Bombay phenotype is genetically type B but functionally type O. What genetic mechanism explains this?

Accepted Answer

Recessive epistasis at the H locus masks the expression of the B allele.

Question 9

Which of the following is true about X-linked inheritance in humans?

Accepted Answer

Males are hemizygous for X-linked genes.

Question 10

Which equation represents the modified phenotypic ratio for dominant epistasis in a dihybrid cross?

Accepted Answer

$$12:3:1$$

Question 11

A man with genotype $$Bb$$ for male-pattern baldness marries a woman with genotype $$Bb. $$What is the probability that their son will be bald?

Accepted Answer

$$3/4$$

Question 12

Which of the following best describes pleiotropy?

Accepted Answer

A single gene affects multiple, seemingly unrelated phenotypic traits.

Question 13

In a complementation analysis, two mutant strains are crossed and the F1 offspring are wild-type. What does this indicate?

Accepted Answer

The mutations are in different genes.

Question 14

Which of the following is an example of sex-limited inheritance?

Accepted Answer

Hen-feathering in chickens, expressed only in females.

Question 15

Which formula represents the expected genotypic ratio for a cross between two heterozygotes in incomplete dominance?

Accepted Answer

$$1:2:1$$

Question 16

Which of the following best explains why males are more likely to express X-linked recessive traits?

Accepted Answer

Males have only one X chromosome, so a single recessive allele will be expressed.

Question 17

Which of the following is true about multiple alleles in a population?

Accepted Answer

Multiple alleles refer to three or more alleles of the same gene present in a population.

Question 18

Which of the following is a correct example of gene interaction resulting in a novel phenotype?

Accepted Answer

Disc-shaped fruit in squash resulting from the interaction of two gene pairs.

Question 19

Which of the following is NOT a possible outcome of a mutation in a gene?

Accepted Answer

Creation of a new chromosome.

Question 20

Which of the following best describes the term 'hemizygous'?

Accepted Answer

Having only one copy of a gene instead of the usual two.

Modification of Mendelian Genetics: Alleles, Dominance, and Complex Inheritance Patterns

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