Question 1

Which person is an obligate carrier of an autosomal-recessive single-gene trait or disorder without expressing the trait or disorder?

Accepted Answer

A) The son of a man with classic hemophilia 
B) The daughter of a woman with Marfan syndrome 
C) The son of a man who expresses a widow's peak hairline 
D) The daughter of a woman who expresses attached earlobes

Question 2

A woman whose father does not have hemophilia gives birth to a son with classic hemophilia. This woman is found to have only 15% of the normal amount of clotting factor VIII (the clotting factor males with hemophilia are missing) and does have abnormal blood-clotting issues. Which phenomenon or factor is most likely responsible for her abnormal clotting factor expression?

Accepted Answer

A) The X chromosome most commonly inactivated in her bone marrow is paternally derived. 
B) The X chromosome most commonly inactivated in her bone marrow is maternally derived. 
C) This woman is demonstrating reduced penetrance of an X-linked-recessive disorder. 
D) This woman is demonstrating full penetrance of an X-linked-recessive disorder.

Question 3

A man whose parents both have brown hair claims that his red beard was inherited from his maternal uncle. Why is this claim incorrect?

Accepted Answer

A) The Y chromosome has no role in scalp, facial, or body hair color. 
B) Genetic traits are transmitted in only a direct vertical direction. 
C) Females cannot transmit facial hair color to their sons. 
D) Hair color is a polygenic trait, not a single-gene trait.

Question 4

Which type of genetic transmission promotes the continued existence of genetic mutations in single genes?

Accepted Answer

A) Autosomal dominant 
B) Autosomal recessive 
C) Codominant 
D) Sex-linked

Question 5

What is the expected expression of a monogenic trait that has its locus on the Y chromosome?

Accepted Answer

A) Females never inherit the trait. 
B) Females inheriting the trait will be carriers. 
C) Males inherit the trait in a dominant pattern of expression; females inherit the trait in a recessive pattern of expression. 
D) Females inherit the trait in a dominant pattern of expression; males inherit the trait in a recessive pattern of expression.

Question 6

A baby boy is born with six toes (polydactyly) on his right foot, a trait that neither parent has but one that the paternal grandfather has. What is the bestexplanation for this occurrence?

Accepted Answer

A) The baby's grandfather is really his father. 
B) The baby inherited a recessive allele for this trait from each parent. 
C) The father's phenotype results from incomplete penetrance of a dominant allele. 
D) The baby's phenotype demonstrates a higher level of expressivity than his father's phenotype.

Question 7

If there are 10 possible alleles for the single-gene trait of nose shape, how many alleles can a person with euploid chromosomes inherit from his or her biological parents?

Accepted Answer

A) 1 
B) 2 
C) 4 
D) 5

Question 8

Which statement or factor is a criterion for autosomal-recessive transmission of single-gene traits?

Accepted Answer

A) About 25% of the members of a large kindred with an autosomal-recessive trait will express the trait. 
B) There is no carrier status; if the allele for the trait is present, it is expressed, although the degree of expression can be variable. 
C) Individuals who are heterozygous for an autosomal-recessive trait have minimal risk for transmitting the allele to their offspring. 
D) The degree of expression of an autosomal-recessive trait or disorder in a homozygous individual is directly related to the penetrance of the trait.

Question 9

Mating of a yellow male parakeet with a blue female parakeet resulted in 18 offspring. Four (two males; two females) had blue feathers, and 14 (eight femalesand six males) had yellow feathers. What allelic combinations and mode of inheritance can you determine from the evidence of the feather colors expressed?

Accepted Answer

A) Yellow allele dominant; blue allele recessive; autosomal 
B) Yellow allele recessive; blue allele dominant; autosomal 
C) Yellow allele dominant; blue allele recessive; sex-linked 
D) Yellow allele recessive; blue allele dominant; sex-linked

Question 10

Agirl of normal stature is born to two parents with achondroplasia who have very short stature, especially disproportionately short arms and legs. What is theprobability (by Punnett square analysis) that any pregnancy this girl eventually has will result in the birth of an infant with achondroplasia if her partner also has normal stature?

Accepted Answer

A) Three out of four (75%) 
B) Two out of four (50%) 
C) One out of four (25%) 
D) Zero out of four (0%)

Question 11

On a five-generation pedigree, which feature distinguishes an X-linked-dominant disorder in which males and females are equally affected from an autosomal-recessivepattern of inheritance?

Accepted Answer

A) The disorder is not apparent until adulthood. 
B) Unaffected individuals do not have affected children. 
C) There are no instances of an affected father transmitting the disorder to his son. 
D) Unaffected parents (who do not express the disorder) do have affected children.

Question 12

Which factor allows inheritance patterns for a specific trait or health problem to be traced from one family generation to another?

Accepted Answer

A) Pleiotropy 
B) Allele segregation 
C) Regression to the mean 
D) Gene-environment interaction

Question 13

What can be inferred about a genetic disorder that, when it occurs in monozygotic twins, affects one twin 80% of the time and affects both twins only 20% of the time?

Accepted Answer

A) Expression of homologous genes is influenced by the gender of the parent who contributed them. 
B) Nongenetic factors can influence the expression of identical alleles. 
C) The mutation occurred in a somatic cell rather than a germ cell. 
D) Mutation repair is incompletely penetrant.

Question 14

Which statement about the X chromosome is true?

Accepted Answer

A) Most of the X chromosome genes encode proteins that have no role in female sexual development. 
B) Heterozygous females are more severely affected by X-linked-dominant disorders than heterozygous males. 
C) When dominant alleles are present on the X chromosome, they are expressed in a recessive manner in the hemizygous state. 
D) When males have the unusual condition of two Y chromosomes and are missing the X chromosome, all physiologic function remains normal.

Question 15

In which situation are phenotype and genotype always the same?

Accepted Answer

A) X-linked-recessive traits 
B) X-linked-dominant traits 
C) Autosomal-recessive traits 
D) Autosomal-dominant traits

Question 16

What is the expected outcome of any pregnancy or child produced by two parents who are each heterozygous for the Huntington disease allele?

Accepted Answer

A) The couple cannot produce children who are unaffected. 
B) Homozygous offspring will express the disease in childhood instead of as an adult. 
C) A child who is homozygous for the mutated alleles is not likely to transmit the disorder to his or her children. 
D) Because of the possibility of incomplete or low penetrance, an unaffected offspring could have an affected child.

Exam 4: Patterns of Inheritance