Question 1

Which of the following best describes the allelic series for coat color in rabbits, as shown in the image, and the type of mutation associated with the albino phenotype?

Accepted Answer

The allelic series is C \u003e cch \u003e ch \u003e c, and the albino phenotype is caused by a null (amorphic) mutation.

Question 2

A rabbit with genotype $$C^{ch}c$ is crossed with a rabbit of genotype $$cchc$$. What is the expected coat color phenotype of their offspring?

Accepted Answer

All offspring will be Himalayan or Chinchilla, depending on the dominance hierarchy.

Question 3

Which of the following best explains why the Himalayan allele ($$ch) in $$rabbits produces a temperature-sensitive phenotype?

Accepted Answer

The $$ch$$ allele encodes a hypomorphic enzyme that is only active at lower temperatures, resulting in pigment production in cooler body regions.

Question 4

In the pedigree shown, individuals display a range of symptoms including premature graying, white forelock, hearing loss, and different-colored eyes. Which genetic concept does this illustrate?

Accepted Answer

Pleiotropy, where a single gene affects multiple distinct traits.

Question 5

A gene mutation results in a protein that interferes with the function of the normal protein in a multimeric complex. What type of mutation is this?

Accepted Answer

Dominant negative mutation

Question 6

A person with genotype $$I^A I^B$$ for the ABO blood group system will have which blood type and why?

Accepted Answer

Type AB, because both $$I^A$$ and $$I^B$$ alleles are codominant and both antigens are expressed.

Question 7

Which of the following best describes incomplete penetrance?

Accepted Answer

Not all individuals with a particular genotype display the expected phenotype.

Question 8

A genetic disorder is only expressed in males, even though the gene is present in both sexes. This is an example of:

Accepted Answer

Sex-limited trait

Question 9

Which of the following best describes the molecular basis of dominance for a wild-type allele that is haplosufficient?

Accepted Answer

One copy of the wild-type allele produces enough functional protein for a normal phenotype.

Question 10

A child is born with phenylketonuria (PKU), but does not develop neurological symptoms due to a special diet. This is an example of:

Accepted Answer

Gene–environment interaction

Question 11

In a dihybrid cross involving two genes that interact epistatically, the observed phenotypic ratio is 9:7 instead of the expected 9:3:3:1. What does this suggest about the gene interaction?

Accepted Answer

Both genes are required for the same phenotype, and a mutation in either gene results in the same mutant phenotype.

Question 12

A mutation in the β-globin gene causes sickle cell disease, which affects red blood cells, causes anemia, and leads to organ damage. This is an example of:

Accepted Answer

Pleiotropy

Question 13

Which of the following best describes a neomorphic mutation?

Accepted Answer

A mutation that results in a novel gene function not seen in the wild-type.

Question 14

A goat displays a chin beard only if it is male, even though both sexes carry the gene. This is an example of:

Accepted Answer

Sex-influenced trait

Question 15

If a gene has three alleles with a dominance hierarchy of $$A \u003e B \u003e C$$, which genotype will display the phenotype associated with allele B?

Accepted Answer

$$BB$$ only

Question 16

Which of the following is true about codominance?

Accepted Answer

Both alleles are fully expressed in the heterozygote, resulting in a distinct phenotype.

Question 17

A leaky (hypomorphic) mutation in a gene results in which of the following?

Accepted Answer

Partial loss of gene function, with phenotype severity depending on the level of activity.

Question 18

Which of the following best describes variable expressivity?

Accepted Answer

Individuals with the same genotype show a range of phenotypic expression.

Question 19

In a population, a gene has four alleles with the following dominance hierarchy: $$A \u003e B \u003e C \u003e D. $$Which genotype will display the phenotype associated with allele C?

Accepted Answer

$$CC or$$ $$CD$$

Question 20

Which of the following is an example of a gene–gene interaction that modifies Mendelian ratios?

Accepted Answer

Epistasis, where one gene masks or modifies the effect of another gene.

Gene Interaction and Extensions to Mendelian Inheritance: Study Notes

Study Guide - Practice Questions

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