chapter 4 patterns of inheritance

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.

C

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

C

Which common health problem has the highest heritability estimate? A. Hypertension B. Peptic ulcer disease C. Congenital heart disease D. Schizophrenic behavior

D

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

D

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.

C

What is the risk for a person to inherit an autosomal-dominant genetic disease-causing allele from a parent who is heterozygous if the disorder has a penetrance factor of 75%? A. 100% B. 75% C. 50% D. 25%

C

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.

C

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 a higher probability of having a child who does not express the trait at all. B. A person with high expressivity of the trait has a greater risk of 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.

C

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? 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.

A

An infant with type B blood is born to parents who both have O blood. What genetic phenomenon is responsible for this unusual blood type expression? A. Decreased penetrance of a dominant trait B. Variable expressivity of a recessive trait C. Inactivation of both parents' X chromosomes D. Failure of one parent's blood-type gene alleles to segregate

A

Is it possible for two parents with achondroplasia to have a child who is of normal stature? A. Yes, because the disorder is autosomal dominant, and if both parents are heterozygous, the child could inherit two normal stature gene alleles. B. Yes, if the parent who is homozygous for the gene mutation demonstrates variable expressivity of the health problem. C. No, because the disorder is autosomal recessive, and the child can only inherit two mutated gene alleles for the health problem. D. No, because homozygosity for this health problem is lethal.

A

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 females and six males) had yellow feathers. What allelic combinations and mode of inheritance can you determine from the evidence of the feather colors expressed? 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

A

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.

A

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.

A

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.

A

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.

A

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.

A

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.

B

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

B

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 the expression of identical alleles. C. The mutation occurred in a somatic cell rather than a germ cell. D. Mutation repair is incompletely penetrant.

B

What is the most likely explanation for the expression of responses related to pleiotropy? A. The same gene may have more than one chromosome locus. B. The protein coded for by the single gene is an important component of more than one tissue. C. The silencing of a gene allele inherited from one parent is expressed differently depending on which parent contributed the silenced allele. D. The same disorder may have an autosomal-dominant inheritance pattern, an autosomal-recessive inheritance pattern, and an X-linked-recessive inheritance pattern.

B

Which factor allows inheritance patterns for a specific trait or health problem to be traced from one family generation to another? A. Pleiotropy B. Allele segregation C. Regression to the mean D. Gene-environment interaction

B

Which situation is an example of modifier gene action? A. A mother and father both have type O blood, and their son is born with type B blood. B. Two children in the same family both have sickle cell disease, but one child has more severe symptoms than the other. C. Monozygotic twins separated at birth and raised in two different countries are of different heights (3 inches) and different weights (25 pounds). D. A woman who has a gene mutation for diabetes mellitus type 2 delays the onset of the disease by exercising and maintaining a normal weight.

B

Which statement is a criterion for an autosomal-dominant pattern of inheritance of a specific trait or characteristic that is highly penetrant? A. Carriers for the trait may express it but do not necessarily express the trait. B. Unaffected family members do not transmit the trait to their children. C. Genotypes of individuals expressing the trait must be homozygous. D. The trait appears only among male offspring of female carriers.

B

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.

B

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

B

With which type of inheritance pattern does the trait or disorder usually first appear among siblings rather than in parents of affected children? A. Autosomal dominant B. Autosomal recessive C. X-linked dominant D. Codominant

B

If a man with classic hemophilia (X-linked recessive) has children with a woman who is a carrier for the disorder, what is the expected risk pattern? A. All sons will be unaffected; all daughters will be carriers. B. All sons will be carriers; all daughters will be affected. C. All sons have a 50% risk of the disorder; daughters will all either be affected or carriers. D. All sons will be carriers; daughters have a 50% chance of being a carrier and a 50% chance of being unaffected.

C

Mating of a female rabbit with a long tongue with a male rabbit that had a short tongue resulted in 12 offspring. Two had long tongues, two had short tongues, and eight had medium-length tongues. Which allele combinations explains the tongue lengths of the offspring? A. Short tongue dominant; long tongue recessive B. Short tongue recessive; long tongue dominant C. Short tongue dominant; long tongue dominant D. Short tongue dominant; long tongue X-linked recessive

C

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

C

Which trait or disorder has both an autosomal-dominant form and an autosomal-recessive form? A. Widow's peak B. Diabetes mellitus type 2 C. Polycystic kidney disease D. Taste sensitivity to phenylthiocarbamate (PTC)

C

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%)

D

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

D

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.

D

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.

D

Which genetic disorder has both an autosomal-dominant and an autosomal-recessive form? A. Syndactyly B. Phenylketonuria C. Long QT syndrome D. Retinitis pigmentosa

D