chap 6
The following pedigree illustrates the inheritance of Nance-Horan syndrome, a rare genetic condition in which affected persons have cataracts and abnormally shaped teeth. Assume that the trait is X-linked recessive. If III-2 and III-7 were to mate, what is the probability that their first child would have Nance-Horan syndrome?
1/2
Many people fear that genetic testing could lead to discrimination in which areas?
All of the above
Consider the pedigree shown in Figure 6.3. If individuals IV-4 and IV-5 mated and produced a child, what is the probability that the child would have Waardenburg syndrome?
0
Consider the pedigree shown in Figure 6.3. If individual IV-7 married a person who was unaffected with Waardenburg syndrome, what is the probability that their first child would have Waardenburg syndrome?
1/2
Ectrodactyly is a rare condition in which the fingers are absent and the hand is split. Ademar Freire-Maia reported the appearance of ectrodactyly in a family in São Paulo, Brazil, whose pedigree is shown here. What mode of inheritance is most likely?
Autosomal recessive
What is the most likely mode of inheritance of the trait shown in the pedigree below, assuming that the trait is rare and fully penetrant?
Autosomal recessive
Which observation from adoption studies most strongly indicates that genetic differences among people contribute more to differences in a phenotype than do environmental differences?
Adopted persons are more similar on average to their biological parents than to their adoptive parents
Which feature of direct-to-consumer genetic tests are public health officials and consumer advocates least concerned about?
All of the above are concerns
In a pedigree, a rare trait appears in both sexes with equal frequency, and affected offspring often has one affected parent. What is the most likely mode of inheritance?
Autosomal dominant
What is the most likely mode of inheritance of the rare trait shown in the pedigree below?
Autosomal dominant, sex-limited to males
On the basis of the concordance rates shown in Table 6.2, what conclusion can you make about the influence of genetic and environmental factors on variation in rheumatoid arthritis?
B and C
M. T. Tsuang and colleagues studied drug dependence in male twin pairs (M. T. Tsuang et al, American Journal of Medical Genetics 67:473-477, 1996). They found that 82 out of 313 monozygotic twins were concordant for abuse of one or more illicit drugs, whereas 40 out of 243 dizygotic twins were concordant for the same trait. On the basis of these data, what conclusion can you make concerning the roles of genetic and environmental factors in drug abuse?
Both genetic and environmental differences contribute to drug abuse.
Both members of an expecting couple are carriers of Tay-Sachs disease, which is an autosomal recessive condition that causes deterioration of nervous function within several months after birth, and usually death by age 4. The couple wants to avoid having a child with Tay-Sachs disease and a DNA test is available to detect the mutant allele. It is early in the pregnancy, and the couple is willing to abort the fetus if it is homozygous for the allele that causes Tay-Sachs disease. However, the couple wishes to have the abortion performed as early as possible if one is to be done. Which would be the most appropriate test to determine the fetus' genotype?
Chorionic villus sampling
The Genetic Information Nondiscrimination Act prohibits insurance companies from denying which kind(s) of coverage to individuals based on results of genetic tests?
Health insurance
Suppose that a harmful autosomal recessive condition is found at a particularly high frequency within a certain population. Public health officials would like to reduce the incidence of the condition in the population using genetic testing and genetic counseling. Which of the following programs would be most appropriate and most effective in achieving the desired outcome?
Heterozygote screening
Which of the following individuals shown in the pedigree below has an unexpected phenotype if the trait is inherited as an X-linked recessive trait?
II-2
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, Annals of Human Genetics 20:177-231, 1956). Inherited deafness in humans is generally thought to result from autosomal recessive mutations.
III-7 and III-9 are homozygous for recessive alleles at two different loci that control hearing ability such that there is complementation in their offspring
Many genetic studies, particularly those of recessive traits, have focused on small isolated human populations, such as those on islands. Which of the following is a major advantage that isolated populations might provide for the study of recessive traits?
Inbreeding, which is more common in small populations, will tend to increase the frequency of recessive conditions, allowing for more cases to be examined
Which statement correctly distinguishes monozygotic from dizygotic twins?
Monozygotic twins result from the splitting of the early embryo into two sections, while dizygotic twins result from two different fertilization events.
Phenylketonuria (PKU) is an autosomal recessive condition that can lead to mental retardation. It is caused by an enzyme deficiency that interferes with phenyalanine metabolism, causing a byproduct to accumulate to levels that are toxic to brain development. Intellectual disability due to PKU can be prevented by a special diet that strictly restricts intake of phenylalanine but the diet must be started soon after birth to be effective. Which of the following would be the most appropriate and cost-efficient way of identifying individuals who need the special diet?
Newborn screening
Which feature(s) would allow you to distinguish between X-linked recessive inheritance and autosomal recessive inheritance in a pedigree?
Normally, more males than females are affected by an X-linked recessive trait.
Which observation most strongly suggests that genetic differences contribute more to phenotypic differences among people than do environmental differences?
Significantly higher concordance values in monozygotic twins than in dizygotic twins
Which feature(s) would allow you to distinguish between autosomal dominant inheritance and Y-linked inheritance in a pedigree of a rare trait?
The trait is passed from a father to all of his sons in Y-linked inheritance but usually to half his sons and daughters in autosomal dominant inheritance.
What is the main reason that geneticists devote so many resources to studying genetics in humans?
We want to understand the many aspects of human health, physiology, and behavior that are influenced by genes.
What is the most likely mode of inheritance of the trait shown in the pedigree below, assuming that the trait is relatively rare in the general population and fully penetrant?
X-linked dominant
Dent disease is a rare disorder of the kidney in which reabsorption 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. American Journal of Human Genetics 76:260-267, 2005). On the basis of this pedigree, what is the most likely mode of inheritance for the disease?
X-linked recessive
In a pedigree, a rare trait appears much more frequently in males than in females, and affected offspring are usually born to unaffected parents. What is the most likely mode of inheritance?
X-linked recessive
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, Annals of Human Genetics 20:177-231, 1956). Inherited deafness in humans is generally thought to result from autosomal recessive mutations.
Yes, every aspect of the pedigree can be explained by autosomal recessive inheritance, assuming that two different genes are involved
A geneticist studies a series of characteristics in monozygotic twins and dizygotic twins, obtaining the following concordances. Based on the data, variation in which characteristic appears to be controlled almost exclusively by genetic variation and not by environmental variation?
eye color
A geneticist studies a series of characteristics in monozygotic twins and dizygotic twins, obtaining the following concordances. Based on the data, variation in which of the following characteristics appears to be controlled the least by genetic variation?
handedness
Noninvasive prenatal diagnosis can be carried out much earlier during pregnancy than amniocentesis or chorionic villus sampling and may be become routine clinically in the near future. Which of the following ethical issues will likely be decreased by the wide-spread practice of noninvasive prenatal diagnosis carried out early in the pregnancy?
the number of healthy fetuses that will be harmed from increased testing
Which of the following is not a common reason for seeking genetic counseling?
A 30-year-old woman wants to get pregnant by her 50-year-old husband.
Which factor does NOT complicate the task of studying the inheritance of human characteristics
All of the above will complicate the task of studying the inheritance of human characteristics.
A man with a specific unusual genetic trait marries an unaffected woman. Which of the following correctly states the expected incidence of the trait in their children if the trait is X-linked dominant? Assume that the trait is rare and fully penetrant.
All of the daughters and none of the sons will be affected.
A man with a specific unusual genetic trait marries an unaffected woman. Which of the following correctly states the expected incidence of the trait in their children if the trait is Y-linked? Assume that the trait is rare and fully penetrant.
All of the sons and none of the daughters will be affected.
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, American Journal of Human Genetics 76:327-333, 2005). What is the most likely mode of inheritance for migraine headaches in these families?
Autosomal dominant
The following pedigree illustrates the inheritance of ringed hair, a rare condition in which each hair is differentiated into light and dark zones. What mode of inheritance is most likely for the ringed-hair trait in this family?
Autosomal dominant
Which mode(s) of inheritance explain the pattern of occurrence of a rare trait in the pedigree below?
Autosomal dominant, sex-limited to males
Which conclusions are supported by Figure 6.13?
Biological fathers of obese children have higher BMI than biological fathers of thin children.
Mary and Jeff's son Todd has hemophilia. Mary is now pregnant, and they seek the services of a genetic counselor to assess the risk of having a second child who has hemophilia. The genetic counselor asks them to research their family history for the purpose of building a pedigree. Mary learns that her mother's father also had hemophilia. After the pedigree is constructed, who should be considered the proband
Mary and Jeff's son Todd should be considered the proband because he is the first affected family member to come to the attention of the genetic counselor
Which technique would be used in combination with in vitro fertilization to allow a couple, both of whom are carriers of a recessive disorder, to establish a pregnancy with a genetically healthy embryo?
Preimplantation genetic diagnosis
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. The table below indicates the percentages of adopted persons with schizophrenia who have at least one biological and/or adoptive parent with schizophrenia.
The data indicate that genes play a major role in schizophrenia because adopted persons with schizophrenia are much more likely to have a biological parent (12%) with schizophrenia than they are to have a adoptive parent (2%) with schizophrenia.
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. What is the most likely mode of inheritance for color blindness in this family?
X-linked recessive
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, American Journal of Human Genetics 74:1043-1050. 2004). Which of the following modes of inheritance best fits the pattern observed in the pedigree? Note that the phenotypes in generation 1 are not known.
Autosomal dominant
Which of the following is typically NOT expected to be associated with genetic counseling?
Directive advice about reproductive decisions
Dizygotic twinning often runs in families and its frequency varies among ethnic groups, whereas monozygotic twinning rarely runs in families and its frequency is quite constant among ethnic groups. These observations have been interpreted as evidence of a genetic basis for variation in dizygotic twinning but for little genetic basis for variation in monozygotic twinning. What is the most likely explanation for these differences in the genetic tendencies of dizygotic and monozygotic twinning?
Dizygotic twinning might be influence by genetic factors involving the mother's genotype, while monozygotic twinning is a chance, accidental event occurring development.
In a pedigree, a rare trait appears in both sexes with equal frequency, and affected offspring are usually born to unaffected parents. What is the most likely mode of inheritance?
autosomal recessive
The following pedigree illustrates the inheritance of Nance-Horan syndrome, a rare genetic condition in which affected persons have cataracts and abnormally shaped teeth. On the basis of this pedigree, what is the most likely mode of inheritance of Nance-Horan syndrome?
X-linked recessive
Dent disease is a rare disorder of the kidney, in which reabsorption 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, American Journal of Human Genetics 76:260-267, 2005). If the disease is inherited as an X-linked recessive, what is the genotype of II-7?
XD XD