Deck 4: Patterns of Inheritance

Question 1

Why are dizygotic twins less likely to show concordance for a monogenic trait than monozygotic twins?

A)Dizygotic twins share fewer allele sequences in common than monozygotic twins.
B)It is possible for dizygotic twins to have different fathers and monozygotic twins always have the same father.
C)Gene expression in monozygotic twins is less influenced by environmental factors than that of dizygotic twins.
D)Because of their identical appearance,monozygotic twins are more likely to be raised together and share a common environment than are dizygotic twins.

Answer 1

Dizygotic twins share fewer allele sequences in common than monozygotic twins.

Question 2

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

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.

Answer 2

Genetic traits are transmitted in only a direct vertical direction.

Question 3

Which genetic disorder has both an autosomal dominant and an autosomal recessive form?

A)Syndactyly
B)Phenylketonuria
C)Long QT syndrome
D)Retinitis pigmentosa

Answer 3

Retinitis pigmentosa

Question 4

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 best explanation for this occurrence?

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 5

In which situation are phenotype and genotype always the same?

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

Question 6

Which statement regarding inheritance of an autosomal dominant gene allele with known variability in expressivity is true?

A)A person with low expressivity of the trait has higher probability for having a child who does not express the trait at all.
B)A person with high expressivity of the trait has a greater risk for having a child who expresses the trait to an even greater degree.
C)The degree of expressivity of a given autosomal dominant trait with known variability cannot be predicted by analyzing parental expression.
D)The degree of expressivity of a given autosomal dominant trait with known variability is greater when the transmitting parent is the same sex as the child.

Question 7

Which situation most closely represents an example of "regression to the mean?"

A)Two hearing impaired parents produce a child who has normal hearing.
B)A 40-year-old man whose father developed type 2 diabetes mellitus at age 50 is diagnosed with the disorder.
C)The three children of a mother who has an intelligence quotient (IQ)of 170 all have IQs in the 110 to 120 range.
D)A child whose biologic parents are thin is adopted by a family whose members are obese and eventually becomes overweight.

Question 8

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

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.

Question 9

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?

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

Question 10

A woman (Adele)has three daughters (Barbara,Brenda,Beverly)with a man (Adam)who is color-blind.Barbara has a daughter (Carol)and a son (Cliff)who have normal color vision.Brenda has no children.Beverly has two sons (Carl,Charlie)who are both color-blind.To which genetic generation do Carl and Charlie belong?

A)P₁
B)P₂
C)F₁
D)F₂

Question 11

What is the most obvious expected finding when analyzing a four-generation pedigree for sex-linked dominant transmission of a trait?

A)Transmission is never father to son.
B)Females are affected at twice the rate of males.
C)An unaffected mother can transmit the trait to her sons.
D)An affected mother always transmits the trait to all her children equally.

Question 12

When calculating the recurrence risk for a complex possibly polygenic disorder with a couple who already have one child with the disorder,which additional factor has the greatest impact on increasing this risk?

A)The child with the disorder is male and the overall incidence of the disorder is twice as high in males than females.
B)Both the mother and the father are heavily exposed to a variety of chemicals in their workplaces.
C)The father has a nephew with a mild form of the same disorder.
D)The mother has a brother who also has the same disorder.

Question 13

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

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 14

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

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

Question 15

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

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 16

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

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 17

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?

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

Question 18

Which statement or condition best reflects multifactorial inheritance?

A)A mutation in a single gene results in the expression of problems in a variety of tissues and organs.
B)The susceptibility to a problem is an inherited trait but development of the problem is related to environmental conditions.
C)A mutated gene is inherited but the results of expression of that gene are not evident until middle or late adulthood.
D)Several genes are responsible for the mechanism of hearing,and a mutation in any one of them results in hearing impairment.

Question 19

A girl of normal stature is born to two parents with achondroplasia who have very short stature,especially disproportionately short arms and legs.What is the probability (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?

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 20

Which statement reflects the criterion for autosomal dominant transmission of single gene traits?

A)The risk for a person who is homozygous for the trait to transmit the trait to his or her children is 100% with each pregnancy.
B)The trait often remains unexpressed within a kindred for many generations until a change in environment promotes its expression.
C)Males in a kindred are more likely to express the trait when the mother has the trait,and females in a kindred are more likely to express the trait when the father has the trait.
D)Females in a kindred are more likely to express the trait when the mother has the trait,and males in a kindred are more likely to express the trait when the father has the trait.

Question 21

What is the implication of the Agouti mice experiments with methylation?

A)Methylation has the potential to affect the expression of polygenic traits but not monogenic traits.
B)Epigenetic changes in gene expression can become more severe with each new generation.
C)Some variations in phenotype are not related to DNA allele sequence variation.
D)Epigenetic changes are reversible when DNA repair mechanisms are active.

Question 22

Which common health problem has the highest heritability estimate?

A)Hypertension
B)Peptic ulcer disease
C)Congenital heart disease
D)Schizophrenic behavior

Question 23

Which statement about the X chromosome is true?

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 24

What is the significance of a shift to the left in the threshold value of liability in a threshold of liability model for the expression of a complex health problem with genetic influences?

A)The threshold required for disease expression increases as the population ages.
B)The number of affected individuals within the population has decreased.
C)The population examined for the potential problem is getting larger.
D)The threshold required for disease expression is lower.

Question 25

How does histone modification alter gene expression?

A)Modified histones result in increased DNA methylation,which increases transcription of genes in that area.
B)In areas where histones are modified the DNA is more tightly wound and genes are not transcribed.
C)Histone modification results in an increase in microRNA production,which inhibits gene expression by preventing translation.
D)Histone modification results in an increase in microRNA production,which promotes gene expression by enhancing translation.