Chapter 6

Question 1

Two parents are phenotypically normal, but one of their four biological children has a typical autosomal recessive trait. The other three children are phenotypically normal. It is very likely that

a. the affected child is a girl.
b. the affected child is a boy.
c. the trait was expressed by one of the grandparents of the children.
d. the parents are both heterozygous for the trait.
e. if the affected child eventually marries a phenotypically normal spouse, all of the their children will have the trait.

Answer 1

d. the parents are both heterozygous for the trait.

Question 2

Which of the following descriptions of a Y-linked trait in humans is correct?

a. All the sons of an affected father will be affected with the trait.
b. Half the sons of a mother whose father was affected with the trait will be affected.
c. Half the sons of an affected father will not be affected with the trait and the other half will be infertile.
d. All the daughters of an affected father will be phenotypically normal themselves but half of their own sons will be affected with the trait.
e. The parents of an affected man likely were both phenotypically normal.

Answer 2

a. All the sons of an affected father will be affected with the trait.

Question 3

Which of the following statements is incorrect concerning an X-linked recessive trait in humans?

a. An affected man often has phenotypically normal parents.
b. All the sons of an affected woman will be expected to be affected.
c. An affected woman almost always has an affected mother.
d. An affected man usually has a mother who carries the recessive allele.
e. A phenotypically normal woman whose father was affected is likely to be heterozygous for the condition.

Answer 3

c. An affected woman almost always has an affected mother.

Question 4

In pedigree analysis, consanguinity refers to

a. mating between two heterozygous carrier parents.
b. the realization that phenotypes between children and grandparents being often more closely related than between children and parents.
c. mating between two closely related parents.
d. a situation where the children of two parents are adopted.
e. a situation where only one individual in the entire pedigree is affected with the trait or disorder.

Answer 4

c. mating between two closely related parents.

Question 5

In pedigree analysis, the proband is

a. the individual having the trait or disorder from whom the pedigree is initiated.
b. the medical geneticist who analyzes the pedigree to find the mode of inheritance for the disorder.
c. the parents of the first child in the family to show the trait or disorder.
d. one of the grandparents or great grandparents who are in the first generation of the pedigree.
e. the most common software package that geneticists use to analyze pedigrees.

Answer 5

a. the individual having the trait or disorder from whom the pedigree is initiated.

Question 6

Which term refers to mating between closely related people?

a. Consanguinity
b. Probanding
c. Congenital
d. Concordance
e. Discordance

Answer 6

a. Consanguinity

Question 7

Which of the following is not a typical characteristic of human traits that follow an autosomal recessive inheritance pattern?

a. They often “skip” generations.
b. They appear equally in males and females.
c. Parents of affected children are often phenotypically normal themselves.
d. When affected individuals marry phenotypically normal individuals, their children are often phenotypically normal.
e. All of the above are characteristic of autosomal recessive inheritance.

Answer 7

e. All of the above are characteristic of autosomal recessive inheritance.

Question 8

Which of the following is not a characteristic of X-linked recessive traits in humans?

a. More males than females affected.
b. Approximately one-half of the sons of a female carrier are affected.
c. They cannot be passed from father to son.
d. Phenotypically normal daughters of affected men are always carriers.
e. Affected daughters always have an affected mother.

Answer 8

e. Affected daughters always have an affected mother.

Question 9

Most pedigrees showing the hypothetical human trait show the following characteristics:

Males and females are equally affected.
Two unaffected parents can have an affected child.
In families in which the parents are unaffected but the children are affected, 1/4 of the children are affected.

What is the most likely mode of inheritance for this disorder?

a. Autosomal recessive
b. Autosomal dominant
c. X-linked recessive
d. X-linked dominant
e. Y-linked

Answer 9

a. Autosomal recessive

Question 10

Most pedigrees showing the hypothetical human trait show the following characteristics:

If a phenotypically normal woman with an affected father has children with an unaffected man, half of the sons and none of the daughters are affected.
Affected females always have an affected father and an affected maternal grandfather.
The trait is never passed from father to son.

What is the most likely mode of inheritance for this disorder?

a. Autosomal recessive
b. Autosomal dominant
c. X-linked recessive
d. X-linked dominant
e. Y-linked

Answer 10

a. Autosomal recessive

Question 11

Most pedigrees showing the hypothetical human trait show the following characteristics:

Only males are affected.
Affected fathers always pass the trait to sons.

What is the most likely mode of inheritance for this disorder?

a. Autosomal recessive
b. Autosomal dominant
c. X-linked recessive
d. X-linked dominant
e. Y-linked

Answer 11

e. Y-linked

Question 12

Most pedigrees showing the hypothetical human trait show the following characteristics:

Females are affected twice as frequently as males.
Affected fathers may have affected daughters but never affected sons.
Half the children of affected mothers and normal fathers are affected.

What is the most likely mode of inheritance for this disorder?

a. Autosomal recessive
b. Autosomal dominant
c. X-linked recessive
d. X-linked dominant
e. Y-linked

Answer 12

d. X-linked dominant

Question 13

The ability to roll the tongue is caused by a dominant allele. A woman is a “roller,” but one of her parents is not. What is the woman’s genotype?

a. Homozygous dominant
b. Heterozygous
c. Homozygous recessive
d. Either homozygous recessive or homozygous dominant
e. Cannot be determined from this information

Answer 13

b. Heterozygous

Question 14

The ability to roll the tongue is caused by a dominant allele. A woman is a “roller,” but one of her parents is not. The woman is expecting a child with a man who is a “nonroller.” What is the probability that their first child will be a “roller”?

a. 1/4
b. 0
c. 3/4
d. 1/2
e. 1

Answer 14

d. 1/2

Question 15

June has two brothers with Becker muscular dystrophy (BMD), a X-linked recessive condition that allows affected males to survive into adulthood. Her parents are phenotypically normal. She marries Sheldon who also has BMD. June and Sheldon have a daughter. What is the probability that this daughter will have BMD?

a. Near 0
b. 1/4
c. 1/2
d. 3/4
e. 1/8

Answer 15

b. 1/4

Question 16

Which of the following is not normally used to study the inheritance of human traits or disorders?

a. Pedigree analysis
b. Twin studies
c. Adoption studies
d. All of the above are used in the study of human traits or disorders.
e. None of the above is used in the study of human traits or disorders.

Answer 16

d. All of the above are used in the study of human traits or disorders.

Question 17

If in one study with both monozygotic and dizygotic twins, the concordance value for a neurological disorder was 100% for monozygotic twins. Which of the following statements is correct?

a. The concordance value for dizygotic twins will be also 100%.
b. There will be no phenotypic variation in susceptibility for the disorder for all the pairs of twins in the study.
c. The concordance value for dizygotic twins will be 25%.
d. For dizygotic twins, all the variation in susceptibility for the disorder will be due to environmental factors.
e. All the variation in susceptibility for the disorder for monozygotic twins is due to genetic factors.

Answer 17

e. All the variation in susceptibility for the disorder for monozygotic twins is due to genetic factors.

Question 18

Imagine that a human characteristic is determined by genotype only, with no environmental influence. Based on the amount of shared genetic information in MZ (monozygotic) and DZ (dizygotic) twins, what would you expect the concordance values to be in these two sets of twins?

a. The concordance values would be near 100% for both types of twins.
b. The concordance values would be near 50% for both types of twins.
c. The concordance values should be close to 100% for MZ twins and about 50% for DZ twins.
d. The concordance values should be close to 50% for MZ twins and about 25% for DZ twins.
e. The concordance values should be close to 25% for MZ twins and about 75% for DZ twins.

Answer 18

c. The concordance values should be close to 100% for MZ twins and about 50% for DZ twins.

Question 19

Lucy is 16 weeks pregnant and undergoes maternal serum screening to measure her maternal alpha fetoprotein levels (AFP). Her AFP level is several times higher that normal levels. For which of the following disorders should Lucy be offered additional testing?

a. Trisomy 21, a chromosome abnormality
b. Sickle-cell disease, an autosomal recessive disorder
c. Spina bifida, a neural tube defect
d. Hemophila A, a sex-linked recessive disorder
e. Lucy does not need additional testing for any disorder.

Answer 19

c. Spina bifida, a neural tube defect

Question 20

In an effort to identify the influence of genetic factors on both Type 1 diabetes and Type II diabetes, researchers calculated concordance rates for monozygotic twins. Concordance rates of 30–50% have been found for Type I diabetes with concordance rates of 80% for Type II. For both kinds of diabetes, dizygotic concordance rates were about 15%. What does this information suggest concerning the relative effect of genetic and environmental factors for each type of diabetes?

a. Genetic factors have little or no role in the occurrence of Type I diabetes.
b. Type II diabetes is primarily determined by non-genetic factors.
c. Genetic influences exert a larger role in Type II diabetes than in Type I diabetes.
d. Type II diabetes appears to be caused by a single, unidentified gene.
e. Environmental factors have no role in the occurrence of either type of diabetes.

Answer 20

c. Genetic influences exert a larger role in Type II diabetes than in Type I diabetes.

Question 21

Which of the following is not correctly identified as an advantage is using amniocentesis?

a. It can be used to detect chromosome abnormalities prenatally in the fetus.
b. In some cases, it can be used to obtain fetal DNA so that tests can be done to determine if the fetus may have a particular genetic disorder.
c. It can normally be done as early as the sixth week of pregnancy.
d. It can be used to determine if the fetus may have a neural-tube defect.
e. All of the above are advantage with the use of amniocentesis.

Answer 21

c. It can normally be done as early as the sixth week of pregnancy.

Question 22

Heterozygous genetic screening is used mainly to

a. detect genetic disorders among newborn infants.
b. detect adult members of a particular population who may be heterozygous carriers for recessive disorders.
c. detect in healthy adults the presence of a mutant allele that may predispose them to some serious health problem later in life.
d. detect fetuses who may be heterozygous carriers for recessive disorders and may eventually be at risk of having children of their own with these disorders.
e. detect adults that may be heterozygous for serious autosomal dominant disorders.

Answer 22

b. detect adult members of a particular population who may be heterozygous

Question 23

Which of the following statements is NOT correct concerning newborn screening?

a. It is normally done soon after the birth of a child.
b. It is particularly important to test for serious conditions where there is no treatment available.
c. Most newborn testing is done by collecting a small amount of an infant’s blood and then using it for analysis to detect specific genetic disorders.
d. The genetic disorder phenylketonuria is one of the conditions that is usually tested for with newborn screening.
e. All of the above statements are true.

Answer 23

b. It is particularly important to test for serious conditions where there is no treatment available.

Question 24

Heterozygote screening normally involves

a. testing healthy individuals to see if they possess mutant alleles that may make them ill later in life.
b. testing newborn infants to see if they have a genetic disorder so that they can be treated immediately.
c. examining fetal cells to see if they have a serious genetic disorder so thst the pregnancy can be terminated if the parents so desire.
d. testing to determine if two parents are related to each other.
e. testing adult members of a particular population to identify heterozygous carriers for a recessive disorder.

Answer 24

e. testing adult members of a particular population to identify heterozygous carriers for a recessive disorder.

Question 25

This is a form of prenatal testing that is most commonly performed between the 15th and 18th week of pregnancy. a. Chorionic villus sampling b. Preimplantation genetic analysis c. Amniocentesis d. Heterozygote screening e. Presymptomatic screening

Answer 25

c. Amniocentesis

Question 26

This is a form of prenatal testing that is most commonly performed between the 10th and 12th week of pregnancy and involves the insertion of a soft plastic into the vagina to obtain cells. a. Chorionic villus sampling b. Preimplantation genetic analysis c. Amniocentesis d. Heterozygote screening e. Presymptomatic screening

Answer 26

a. Chorionic villus sampling

Question 27

Which of the following conditions is most commonly screened for in maternal blood tests? a. Phenylketonuria and chromosome abnormalities b. Tay-Sachs disease and neural-tube defects c. Cancer and multiple sclerosis d. Chromosome abnormalities and neural tube defects e. None of the above is detected.

Answer 27

d. Chromosome abnormalities and neural tube defects

Question 28

Fetal cell sorting is a(n) a. method of obtaining fetal cells through amniocentesis. b. method of obtaining fetal cells through chorionic villus sampling. c. procedure for detecting and separating fetal cells from maternal blood cells. d. invasive procedure that allows a physician to directly take blood from the fetus to analyze for genetic conditions. e. method where a fetus who has a genetic condition can be treated before birth by providing it with healthy fetal cells.

Answer 28

c. procedure for detecting and separating fetal cells from maternal blood cells.

Question 29

Preimplantation genetic testing involves a. testing a newborn infant for a genetic disorder immediately after birth. b. testing a single cell of an early embryo for a genetic disorder before the embryo is considered for implanting into the mother’s uterus. c. testing multiple sperm from a man who is heterozygous for a serious genetic disorder and then using only sperm that have normal alleles for in vitro fertilizations. d. removing cells from a fetus and then testing them for a genetic disorder and then allowing abnormal fetuses to be aborted. e. testing primary oocytes (eggs) for genetic disorders before using them in in vitro fertilizations.

Answer 29

b. testing a single cell of an early embryo for a genetic disorder before the embryo is considered for implanting into the mother’s uterus.

Question 30

To establish a successful and cost-effective screening program for detecting adult heterozygous carriers of an autosomal recessive disease, all of the following are important for establishing a successful program for a particular disorder except a. detection of the disorder is possible in the fetus. b. the disease is clinically significant. c. a high-risk population can be identified . d. genetic counseling is provided with the testing. e. an effective treatment is available for the disorder

Answer 30

e. an effective treatment is available for the disorder

Question 31

Which of the following human genes shows signs of recent selection suggesting that it provides some unique human characteristic? a. DMD b. FGFR3 c. FGFR2 d. FOXP2 e. XIST

Answer 31

d. FOXP2

Question 32

Tony, who is not diseased, has a sister with cystic fibrosis (CF). Neither of his parents have CF. Tony is expecting a child with Tina. Tina’s family history is unknown. What is the probability that Tony is heterozygous for the CF gene? Explain your answer.

Answer 32

2/3. Tony’s parents are Aa and Aa. Their children’s genotypes, with probabilities, are: 1/4 AA; 1/4 Aa; 1/4 aA; 1/4 aa. Tony does not have CF, so he cannot be genotype aa. Of the remaining genotypes, 2/3 are heterozygous.

Question 33

Tony, who is not diseased, has a sister with cystic fibrosis (CF). Neither of his parents have CF. Tony is expecting a child with Tina. Tina’s family history is unknown. If the frequency of heterozygotes in the general population is 1/50, what is the probability that Tony and Tina’s child will have CF? Explain each factor in your calculation.

Answer 33

2/3 × 1/50 × 1/4 = 2/600, or 1/300 | Tony: heterozygous) × (Tina: heterozygous) × (homozygous recessive from two heterozygotes

Question 34

Explain the principle behind using concordance values for monozygotic and dizygotic twins to determine the influence of genetic factors on individual differences for a trait.

Answer 34

MZ twins theoretically share 100% genetic information and DZ twins only 50%. So if genotype differences cause most of the variation in the population, concordance values for the characteristic will be high in MZ twins and lower in DZ twins.

Question 35

Researchers studying genetic determination of childhood asthma noted 65% concordance for monozygotic twin pairs in which at least one twin has asthma and 37% concordance for dizygotic twin pairs in which at least one twin has asthma. a. Explain the meaning of 65% concordance for asthma in monozygotic twins. b. Interpret the difference in concordance for asthma between monozygotic and dizygotic twins. c. If genes do influence childhood asthma, how is that 35% of monozygotic twin pairs are discordant for asthma?

Answer 35

a. Sixty-five percent concordance indicates that, in 65% of monozygotic twin pairs in which one twin has asthma, the other twin will also have asthma. b. The significantly higher concordance in monozygotic twins compared to dizygotic twins indicates that genes play a major role in contributing to childhood asthma. The difference can be attributed to the fact that monozygotic twins share 100% of their genes, whereas dizygotic twins only share 50% on average. c. The discordance between monozygotic twins suggests that the environment also plays an important part in determining asthma. Given that the monozygotic twins are genetically identical, their different phenotypes must be due to differences in their developmental environments.

Question 36

Explain what it means for a genetic counselor to use “nondirected counseling.”

Answer 36

Nondirected counseling describes a style of counseling in which the genetic counselor provides information, calculates probabilities, explains risk factors, and explains reproductive options but does not offer their own opinion or bring their own values into the discussion.

Question 37

Describe at least two reasons why testing for a genetic condition might be advantageous.

Answer 37

(1) A person with an inherited genetic condition might start early treatment to lessen the severity of the condition. (2) The symptoms of some genetic conditions can be prevented by early treatment. (3) If a person is at risk for inheriting a genetic condition, testing can alleviate the anxiety associated with uncertainty. (4) Parents who are considering children can determine if they are heterozygous for a homozygous recessive condition. (5) A woman who knows the genotype of the embryo or fetus she is carrying may use the information to decide whether to continue or terminate a pregnancy. (6) A woman who knows the genotype of the embryo or fetus she is carrying may use the information to prepare for the birth of a child with an inherited condition. (7) For embryos produced by in vitro fertilization, genetic testing is used to determine which embryos to implant.

Question 38

A maternal blood-screening test carried out in the second month of a pregnancy indicates a level of α-fetoprotein that is significantly higher than normal. a. What is α-fetoprotein? b. What does a higher than normal level of α-fetoprotein in the mother’s blood indicate? c. Critique the maternal blood screening test—specifically, what are its limitations? d. Given the limitations of the tests, why are they so commonly ordered? e. If you were the doctor who ordered this test, how would you proceed?

Answer 38

a. α-fetoprotein is a protein that is normally created by the fetus during development and is normally present in fetal blood, amniotic fluid, and the mother’s blood during pregnancy. b. A higher than normal level indicates that there might be a problem with development of the fetus. Specifically, high levels are associated with neural-tube defects and certain other common disruptions to fetal development. c. Higher than normal levels of α-fetoprotein are associated with increased risk of genetic or developmental problems, but they do not prove that a problem is present. d. Maternal blood-screening tests are not as invasive or as expensive as more definitive tests (e.g., amniocentesis). e. You should order additional tests to confirm or rule out the presence of a developmental problem. These tests might include additional blood tests, ultrasound, amniocentesis, and CVS.