Medical Genetics Test Bank Chapter 3 (Genetic Variation: Its Origin and Detection)

1- Which of the following would not tend to raise mutation rates for single-gene disorders in humans?

A) CG dinucleotides within the gene

B) elevated paternal age

C) caffeine exposure

D) large genes

E) all of the above are known to raise mutation rates in humans

... Answer is C)

2- Which of the following diseases results from faulty DNA repair?

A) neurofibromatosis type 1

B) retinoblastoma

C) xeroderma pigmentosum

D) osteogenesis imperfecta

E) hemophilia A

... Answer is C)

3- Which of the following does not pertain to cystic fibrosis (CF)?

A) consanguinity is commonly seen in parents with CF offspring

B) variable expression

C) more than one mutation at the CF locus can cause the disease

D) potential candidate for gene therapy

E) pleiotropy

... Answer is A)

4- Which of the following is not true of Huntington disease?

A) triplet repeat expansion is observed

B) age of onset is delayed

C) choreic movements are seen

D) recurrence risk for offspring of an affected parent is 50%

E) offspring of affected mothers have earlier age of onset than those of affected father

... Answer is E)

5- A likely explanation for the fact that some 45,X conceptions (Turner syndrome) survive to term is?

A) mosaicism in the fetus

B) delayed age of onset of the disorder

C) germline mosaicism in one of the parents

D) imprinting on the X chromosome

E) incomplete X inactivation

... Answer is A)

6- Which of the following is not a diagnostic feature of neurofibromatosis type 1?

A) neurofibromas

B) positive family history

C) benign hamartomas of the iris

D) melanomas

E) cafe-au-lait spots

... Answer is D)

7- Which of the following is not true of the dystrophin protein?

A) binds actin

B) binds to sarcoglycan/dystroglycan complex

C) can be assayed to diagnose Duchenne muscular dystrophy

D) is absent in patients having Becker muscular dystrophy

E) composes only a very tiny fraction of the mass of a muscle cell

... Answer is D)

8- In which of the following individuals would you not expect to see a Barr body?

A) XX male

B) 45,X female

C) XY female

D) a and b

E) b and c

... Answer is E)

9- Which of the following is not often seen in the individual with Klinefelter syndrome?

A) webbed neck

B) increased stature

C) diminished IQ (on average)

D) sterility

E) gynecomastia

... Answer is A)

10- What is the most likely explanation for the expression of hemophilia A in a female who is a heterozygote for an X-linked mutation in the factor VIII gene?

A) nonsense mutation causing truncated protein

B) her father is affected, and her mother is a heterozygous carrier

C) a high proportion of the X chromosomes carrying the mutation are active in this female

D) one of her X chromosomes carries the SRY gene

E) X inactivation does not affect the entire chromosome

... Answer is C)

11- Which of the following is least likely to increase the recurrence risk of trisomy 13 in a family?

A) advanced maternal age

B) mother carries a 13/14 Robertsonian translocation

C) father carries a 13/14 Robertsonian translocation

D) germline mosaicism in the mother in which some cells are 47,XX,+13

E) advanced paternal age

... Answer is E)

1- The H-Y antigen is encoded by a gene on the human Y chromosome. Suppose that a variant allele at the H-Y locus is found in one in 1,000 males in a population. What is the gene frequency of this allele in the male population?.

2- Continuing question 1, what is the gene frequency of this allele in the female population?.

3- Hemochromatosis is a common autosomal recessive disorder of iron absorption. The gene frequency is approximately 0.05 (1/20) in some Northern European populations. If the penetrance of the disease-causing genotype is 0.5 in males and 0.2 in females, what is the expected incidence of the disease phenotype in the male and female populations?.

4- List at least three explanations for the pedigree shown below for a Mendelian (single-gene) disease (for each explanation, a 2-3 word phrase is sufficient)..

5- A 25-year-old woman has had three children with Down syndrome. Give two possible explanations (for each explanation, a 2-3 word phrase is sufficient)..

6- a man who is a known heterozygous carrier of a cystic fibrosis mutation marries his half first cousin (see pedigree). What is the probability that this couple will produce a child with cystic fibrosis (autosomal recessive disorder)?.

7- A woman who has normal skin pigmentation has two sisters with oculocutaneous albinism, a fully penetrant autosomal recessive disease. What is the probability that this woman is a heterozygous carrier of the disease gene?.

8- Consider a woman who is a known heterozygous carrier of a mutation that causes PKU (autosomal recessive). What is the probability that her two grandchildren (shown in the pedigree as individuals A and B) are both heterozygous carriers of this PKU-causing allele?.

9- Explain the difference between variable expression and incomplete penetrance. Use at least two disease examples to illustrate your discussion (4-5 sentences should be sufficient)..

10- Explain the concept of imprinting. Use disease examples to illustrate your points..

11- Match the pedigree with the most likely mode of inheritance. Note that complicating factors, such as reduced penetrance, may be present. Assume that the gene frequency of the disorder in the general population is very low. These answers may be used more than once.?

A) autosomal dominant

B) autosomal recessive

C) X-linked recessive

D) X-linked dominant

E) mitochondrial

... Answer is C)

12- Match the pedigree with the most likely mode of inheritance. Note that complicating factors, such as reduced penetrance, may be present. Assume that the gene frequency of the disorder in the general population is very low. These answers may be used more than once.?

A) autosomal dominant

B) autosomal recessive

C) X-linked recessive

D) X-linked dominant

E) mitochondrial

... Answer is A)

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