Question 1

Which of the following best describes a haplosufficient allele?

Accepted Answer

An allele for which one copy is enough to produce the wild-type phenotype in heterozygotes.

Question 2

A patient is diagnosed with phenylketonuria (PKU), an autosomal recessive disorder. Which intervention prevents the expression of the PKU phenotype?

Accepted Answer

Dietary restriction of phenylalanine from infancy.

Question 3

In a population, a gene has four alleles: $$C$$, $$c^{ch}$$, $$c^h$$, and $$c. $$Which genotype would result in a temperature-sensitive coat color phenotype in mammals?

Accepted Answer

$$c^hc^h$$

Question 4

Which of the following is an example of codominance?

Accepted Answer

A heterozygote expressing both A and B antigens on red blood cells.

Question 5

A cross between two pure-breeding white-flowered sweet peas produces all purple F$$_1$$ offspring. The F$$_2$$ generation shows a 9:7 ratio of purple to white flowers. What type of gene interaction is this?

Accepted Answer

Complementary gene interaction

Question 6

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

Accepted Answer

$$9:3:4$$

Question 7

A mutation in a gene produces no functional product and is lethal when homozygous. What is the term for this type of mutation?

Accepted Answer

Null mutation (amorphic)

Question 8

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

Accepted Answer

$$ii$$

Question 9

A goat with genotype $$B_1B_2 is $$bearded if male but beardless if female. What is this an example of?

Accepted Answer

Sex-influenced trait

Question 10

A mutation in a multimeric protein prevents normal interaction of polypeptides, resulting in a 'spoiler' effect. What is this mutation called?

Accepted Answer

Dominant negative mutation

Question 11

Which of the following best describes pleiotropy?

Accepted Answer

A single gene mutation affects multiple distinct traits.

Question 12

A dihybrid cross yields a 15:1 ratio in the F$$_2$$ generation. What type of gene interaction does this indicate?

Accepted Answer

Duplicate gene action

Question 13

Which of the following is true about incomplete penetrance?

Accepted Answer

Some individuals with the genotype do not express the phenotype.

Question 14

A cross between two heterozygous yellow mice ($$A^YA) $$produces a 2:1 ratio of yellow to agouti offspring, with no $$A^YA^Y$$ progeny. What explains the absence of $$A^YA^Y$$ mice?

Accepted Answer

Recessive lethal allele causing embryonic death.

Question 15

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

Accepted Answer

$$12:3:1$$

Question 16

A geneticist performs complementation analysis by crossing two pure-breeding mutants with similar phenotypes. The F$$_1$$ offspring all show the wild-type phenotype. What does this indicate?

Accepted Answer

The mutations are in different genes.

Question 17

Which of the following best describes a neomorphic mutation?

Accepted Answer

A mutation that acquires a novel gene activity not found in the wild type.

Question 18

In summer squash, fruit shape is determined by two genes. Disk-shaped fruit requires at least one dominant allele at both loci, round fruit requires a dominant allele at only one locus, and long fruit requires recessive alleles at both loci. What is the expected F$$_2$$ ratio from a dihybrid cross?

Accepted Answer

$$9:6:1$$

Question 19

Which of the following is an example of gene-environment interaction?

Accepted Answer

A temperature-sensitive enzyme affecting coat color in Himalayan rabbits.

Question 20

Which equation represents the expected phenotypic ratio for dominant suppression in a dihybrid cross?

Accepted Answer

$$13:3$$

4. Gene Interaction and Dominance Relationships

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