Genetics: A Conceptual Approach

Benjamin Pierce

Chapter 6

Pedigree Analysis, Applications, and Genetic Testing - all with Video Answers

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Chapter Questions

Problem 1

What three factors complicate the task of studying the inheritance of human characteristics?

Sidharth Anand

Sidharth Anand

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Problem 2

Who is the proband in a pedigree? Is the proband always found in the last generation of the pedigree? Why or why not?

Jorge Villanueva

Jorge Villanueva

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Problem 3

For each of the following modes of inheritance, describe the features that will be exhibited in a pedigree in which the trait is present: autosomal recessive, autosomal dominant, X-linked recessive, X-linked dominant, and Y-linked inheritance.

Jorge Villanueva

Jorge Villanueva

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Problem 4

How does the pedigree of an autosomal recessive trait differ from the pedigree of an X-linked recessive trait?

Jorge Villanueva

Jorge Villanueva

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Problem 5

Other than the fact that a Y-linked trait appears only in males, how does the pedigree of a Y-linked trait differ from the pedigree of an autosomal dominant trait?

Jorge Villanueva

Jorge Villanueva

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Problem 6

What are the two types of twins and how do they arise?

Jorge Villanueva

Jorge Villanueva

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Problem 7

Explain how a comparison of concordance in monozygotic and dizygot ic twins can be used to determine the extent to which the expression of a trait is influenced by genes or by environmental factors.

KL

Kirsten Landry

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Problem 8

How are adoption studies used to separate the effects of genes and environment in the study of human characteristics?

Jorge Villanueva

Jorge Villanueva

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Problem 9

What is genetic counseling?

Jorge Villanueva

Jorge Villanueva

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Problem 10

Give at least four different reasons for seeking genetic counseling.

Jorge Villanueva

Jorge Villanueva

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Problem 11

Briefly define newborn screening, heterozygote screening. presymptomatic testing, and prenatal diagnosis.

Bryan Valdivia

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Problem 12

Compare the advantages and disadvantages of aminocentesis versus chorionic villus sampling for prenatal diagnosis.

Bryan Valdivia

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Problem 13

What is preimplantation genetic diagnosis?

Jorge Villanueva

Jorge Villanueva

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Problem 14

How does heterozygote screening differ from presymptomatic genetic testing?

Jorge Villanueva

Jorge Villanueva

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Problem 15

What are direct-to-consumer genetic tests? What are some of the concerns about these tests?

Jorge Villanueva

Jorge Villanueva

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Problem 16

What activities do the Genetic Information Nondiscrimination Act prohibit?

Jorge Villanueva

Jorge Villanueva

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Problem 17

How might genetic testing lead to genetic discrimination?

Jorge Villanueva

Jorge Villanueva

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Problem 18

If humans have characteristics that make them unsuitable for genetic analysis, such as long generation time, small family size, and uncontrolled crosses, why do geneticists study humans? Give several reasons why humans have been the focus of so much genetic study.

Jorge Villanueva

Jorge Villanueva

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Problem 19

Joe is color blind. Both his mother and his father have normal vision, but his mother's father (Joe's maternal grandfather) is color blind. All Joe's other grandparents have normal color vision. Joe has three sisters-Patty, Betsy, and Lora-all with normal color vision. Joe's oldest sister, Patty, is married to a man with normal color vision; they have two children, a 9 -year-old color-blind boy and
a 4-year-old girl with normal color vision.
a. Using standard symbols and labels, draw a pedigree of Joe's family.
b. What is the most likely mode of inher itance for color blindness in Joe's family?
c. If Joe marries a woman who has no family history of color blindness, what is the probability that their first child will be a color-blind boy?
d. If Joe marries a woman who is a carrier of the color-blind allele, what is the probability that their first child will be a color-blind boy?
e. If Patty and her husband have another child, what is the probability that the child will be a color-blind boy?

Jorge Villanueva

Jorge Villanueva

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Problem 20

Consider the pedigree shown in Figure 6.3
a. If individual IV-7 married a person who was unaffected with Waardenburg syndrome, what is the probability that their first child would have Waard enburg syndrome? Explain your reasoning.
b. If individuals IV-4 and IV-5 mated and produced a child, what is the probability that the child would have Waardenburg syndrome? Explain your reasoning.

KL

Kirsten Landry

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Problem 21

Many studies have suggested a strong genetic predisposition to migraine headaches, but the mode of inheritance is not clear. L. Russo and colleagues examined migraine headaches in several families, two of which are shown below (L. Russo et al. 2005 American Journal of Human Genetics $76: 327-333$ ). What is the most likely mode of inheritance for migraine headaches in these families? Explain your reasoning.

Jorge Villanueva

Jorge Villanueva

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Problem 22

Dent disease is a rare disonder of the kidney, in which re absorption of filtered solutes is impaired and there is progressive renal failure. R. R. Hoopes and colleagues studied mutations associated with Dent disease in the following family (R. R. Hoopes et al. 2005. American Journal of Human Genetics $76: 260-267$ ).
a. On the basis of this pedigree, what is the most likely mode of inheritance for the disease? Explain your reasoning.
b. From your answer to part $a$, give the most likely genotypes for all persons in the pedigree.

Sana Riaz

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Problem 23

A man with a specific unusual genetic trait marries an unaffected woman and they have four children. Pedigrees of this family are shown in parts $a$ through $e,$ but the presence or absence of the trait in the children is not indicated. For each type of inheritance, indicate how many children of each sex are expected to express the trait by filling in the appropriate circles and squares. Assume that the trait is rare and fully penetrant.
a. Autosomal recessive trait
b. Autosomal dominant trait
c. X-linked recessive trait
d. X-linked dominant trait
e. Y-linked trait

Jorge Villanueva

Jorge Villanueva

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Problem 24

For each of the following pedigrees, give the most likely mode of inheritance, assuming that the trait is rare. Carefully explain your reasoning.

Jorge Villanueva

Jorge Villanueva

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Problem 25

The trait represented in the following pedigree is expressed only in the males of the family. Is the trait Y linked? Why or why not? If you believe that the trait is not Y linked, propose an alternate explanation for its inheritance

Prashant Bana

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Problem 26

The following pedigree illustrates the inheritance of Nance-Horan syndmome, a rare genetic condition in which affected persons have cataracts and abnormally shaped teeth.
a. On the basis of this pedigree, what do you think is the most likely mode of inheritance for Nance-Horan syndrome?
b. If couple III-7 and III - 8 have another child, what is the probability that the child will have Nance-Horan syndrome?
c. If III- 2 and III-7 were to mate, what is the probability that one of their children would have Nance-Horan syndrome?

Miwa Wenzel

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Problem 27

The following pedigree illustrates the inheritance of ringed hair, a condition in which each hair is differentiated into light and dark zones. What mode or modes of inheritance are possible for the ringed-hair trait in this family?

Jorge Villanueva

Jorge Villanueva

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Problem 28

Ectrodactyly is a rare condition in which the fingers are absent and the hand is split. This condition is usually inherited as an autosomal dominant trait. Ademar Freire-Maia reported the appearance of ectrodactyly in a family in São Paulo, Brazil, whose pedigree is shown here. Is this pedigree consistent with autosomal dominant inheritance? If not, what mode of inheritance is most likely? Explain your reasoning.

Jorge Villanueva

Jorge Villanueva

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Problem 29

The complete absence of one or more teeth (tooth agenesis) is a common trait in humans-indeed, more than $20 \%$ of humans lack one or more of their third molars. However, more-severe absence of teeth, defined as missing six or more teeth, is less common and frequently an inherited condition. L. Lammi and colleagues examined tooth agenesis in the Finnish family shown in the pedigree below (L. Lammi. 2004 American Journal of Human Genetics $74: 1043-1050$ ).
a. What is the most likely mode of inheritance for tooth agenesis in this family? Explain your reasoning.
b. Are the two sets of twins in this family monozygotic or dizygotic twins? What is the basis of your answer?
c. If IV-2 married a man who has a full set of teeth, what is the probability that their child would have tooth agenesis?
d. If III-2 and III - 7 married and had a child, what is the probability that their child would have tooth agenesis?

Jorge Villanueva

Jorge Villanueva

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Problem 30

A geneticist studies a series of characteristics in monozygotic twins and dizygotic twins, obtaining the concordances listed below. For each characteristic, indicate whether the rates of concordance suggest genetic influences, environmental influences, or both. Explain your reasoning.
$$\begin{array}{lcc}
& \multicolumn{2}{c} {\text { Concordance (\%) }} \\
\)\cline { 2 - 3 }\( \text { Characteristic } & \text { Monozygotic } & \text { Dizygotic } \\
\text { Migraine headaches } & 60 & 30 \\
\text { Eye color } & 100 & 40 \\
\text { Measles } & 90 & 90 \\
\text { Clubfoot } & 30 & 10 \\
\text { High blood pressure } & 70 & 40 \\
\text { Handedness } & 70 & 70 \\
\text { Tuberculosis } & 5 & 5
\end{array}$$

Sofija Dubianskaja

Sofija Dubianskaja

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Problem 31

On the basis of the concordance rates shown in Table
$6.2,$ is variation in rheumatoid arthritis influenced by genetic factors, environmental factors, or both? Explain your reasoning.

Michela Jacobson

Michela Jacobson

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Problem 32

M. T. Tsuang and colleagues studied drug dependence in male twin pairs (M. T. Tsuang et al. 1996. American Journal of Medical Genetics $67: 473-477$ ). They found that 82 out of 313 monozygotic twins were concordant for abuse of one or more elicit drugs, whereas 40 out of 243 dizygotic twins were concondant for the same trait. Calculate the concordance rates for drug abuse in these monozygotic and dizygotic twins. On the basis of these data, what conclusion can you make concerning the roles of genetic and environmental factors in drug abuse?

CS

Courtney Stuart

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Problem 33

In a study of schizophrenia (a mental disorder including disorganization of thought and withdrawal from reality), researchers looked at the prevalence of the disorder in the biological and adoptive parents of people who were adopted as children; they found the following results:
$$\begin{array}{lcc}
& \multicolumn{2}{c} {\text { Prevalence of schizophrenia }} \\
\)\cline { 2 - 3 } & \( \text { Biological } & \text { Adoptive } \\
\text { Adopted Persons } & \text { parents } & \text { parents } \\
\text { With schizophrenia } & 12 & 2 \\
\text { Without schizophrenia } & 6 & 4
\end{array}$$
What can you conclude from these results concerning the role of genetics in schizophrenia? Explain your reasoning.

Hailey Tomashek

Hailey Tomashek

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Problem 34

Which conclusions are supported by Figure 6.13?
a. Adoptive fathers of obese children have a higher BMI than adoptive fathers of thin children.
b. Adoptive mothers of thin children have lower BMI than adoptive mothers of obese children.
c. Biological fathers of obese children have higher BMI than adoptive fathers of thin children.
d. Both a and b.
e. Both a and c.

Jorge Villanueva

Jorge Villanueva

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Problem 35

What, if any, ethical issues might arise from the widespread use of noninvasive prenatal genetic diagnosis, which can be carried out much earlier than amniocentesis or chorionic villus sampling?

Jorge Villanueva

Jorge Villanueva

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Problem 36

Many genetic studies, particularly those of recessive traits, have focused on small isolated human populations, such as those on islands. Suggest one or more advantages that isolated populations might have for the study of recessive traits.

Jorge Villanueva

Jorge Villanueva

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Problem 37

Draw a pedigree that represents an autosomal dominant trait, sex-limited to males, and that excludes the possibility that the trait is Y linked.

Jorge Villanueva

Jorge Villanueva

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Problem 38

A. C. Stevenson and E. A. Cheeseman studied deafness in a family in Northern Ireland and recorded the following pedigree (A. C. Stevenson and E. A. Cheeseman. $1956 . \text { Annals of Human Genetics } 20: 177-231)$
a. If you consider only generations I through III, what is the most likely mode of inheritance for this type of deafness?
b. Provide a possible explanation for the cross between III.
7 and III-9 and the results for generations IV through V.

Brenda Sanchez

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Problem 39

Dizygotic twinning often runs in families and its frequency varies among ethnic groups, whereas monozygot ic twinning rarely runs in families and its frequency is quite constant among ethnic groups. These observations have been interpreted as evidence for a genetic basis for variation in dizygotic twinning but for little genetic basis for variation in monozygotic twinning. Can you suggest a possible reason for these differences in the genetic tendencies of dizygotic and monozygotic twinning?

Prashant Bana

Numerade Educator