Question 1

Which of the following best describes incomplete dominance, as illustrated by the cross between red and white snapdragon flowers?

Accepted Answer

The heterozygote expresses a phenotype intermediate between the two parental phenotypes.

Question 2

A mutation in the gene encoding the β-globin chain of hemoglobin results in sickle-cell disease. Which type of mutation is this an example of?

Accepted Answer

Loss-of-function mutation

Question 3

In the ABO blood group system, which genotype(s) will result in a person with blood type AB?

Accepted Answer

$$I^A I^B$$

Question 4

A woman with blood type A has a child with blood type O. Which of the following blood types could the father NOT have?

Accepted Answer

Type AB

Question 5

Which of the following best explains the Bombay phenotype in the context of ABO blood groups?

Accepted Answer

A mutation at a different locus prevents the formation of the H substance, masking the ABO phenotype.

Question 6

Which of the following is an example of pleiotropy?

Accepted Answer

Marfan syndrome affecting the eye, skeleton, and cardiovascular system

Question 7

A cross between two mice with genotypes $$BbCc 	imes BbCc$$ produces offspring with the following phenotypic ratio: 9 black : 3 brown : 4 white. What genetic phenomenon does this illustrate?

Accepted Answer

Epistasis

Question 8

Which of the following statements about X-inactivation in female mammals is correct?

Accepted Answer

One X chromosome is randomly inactivated in each cell, forming a Barr body.

Question 9

A genetic disorder shows 90% penetrance. What does this mean?

Accepted Answer

90% of individuals with the mutant genotype show some degree of the phenotype.

Question 10

Which of the following best describes variable expressivity?

Accepted Answer

Individuals with the same genotype show a range of phenotypes.

Question 11

Which of the following is an example of a polygenic trait?

Accepted Answer

Human skin color

Question 12

A man with pattern baldness (genotype $$Bb) $$and a woman without pattern baldness (genotype $$Bb) $$have a son. What is the probability that their son will be bald, given that pattern baldness is sex-influenced and $$B is $$dominant in males?

Accepted Answer

$$1/2$$

Question 13

Which of the following best describes codominance?

Accepted Answer

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

Question 14

A geneticist observes that a mutation is lethal only when homozygous, but heterozygotes display a distinct mutant phenotype. What is this allele called?

Accepted Answer

Recessive lethal allele

Question 15

Which of the following is a real-life example of a dominant lethal mutation?

Accepted Answer

Huntington disease

Question 16

A Drosophila fly is heterozygous for the white gene, but the gene is translocated to a different chromosome location. What phenomenon might alter the expression of the white gene in this fly?

Accepted Answer

Position effect

Question 17

Which of the following best describes the effect of a loss-of-function mutation in an essential gene?

Accepted Answer

It may be tolerated in the heterozygous state but is lethal when homozygous.

Question 18

Which of the following is true about sex-limited inheritance?

Accepted Answer

The phenotype is expressed in only one sex, even though both sexes carry the gene.

Question 19

A person with phenylketonuria (PKU) can avoid the disease phenotype by following a special diet. What does this illustrate?

Accepted Answer

The influence of environmental factors on phenotypic expression

Question 20

Which of the following best describes the concept of hemizygosity?

Accepted Answer

Having only one copy of a gene in a diploid organism, as with X-linked genes in males

CH4: Extensions of Mendelian Genetics: Complex Patterns of Inheritance

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