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1) A 25-year-old man and his 24-year-old wife have a baby boy who has a problem with bowel obstruction soon after birth, but an otherwise uneventful infancy. In childhood, however, their son has a succession of respiratory tract infections. Laboratory workup fails to reveal an immunologic deficit. Their daughter, born two years later, does not have these problems. There is no family history for this disorder. Their son is infertile; their daughter gives birth to a son and daughter, both of whom are not affected by this disorder. Which of the following is the most likely pattern of inheritance for this family?
A Autosomal dominant

B Autosomal recessive

C Dominant negative

D X-linked recessive

E Spontaneous new mutation

2) A missense mutation is found to have an incidence of 1/100,000 persons. It involves a single amino acid in a gene encoding for an enzyme. This mutation is most likely to be manifested by which of the following patterns of inheritance?

A Autosomal dominant

B Autosomal recessive

C X-linked recessive

D Dominant negative

E Multifactorial

5) A 2-year-old child is brought to the physician by his parents because he is not growing normally. Both parents are tall (father 193 cm, or 6' 4" and mother 180 cm, or 5' 11") but the child is below the 5th percentile for height for his age. On physical examination his decreased height is primarily due to shortened extremities. The child is neurologically normal, and he is developing motor and verbal skills normally. There is no family history of other children being small on either side of the family. The parents are pointing fingers at each other in regard to infidelity. Which of the following genetic conditions is most likely to explain this set of findings?

A Autosomal recessive condition

B X-linked recessive condition

C Variable expressivity

D Uniparental disomy

E Spontaneous new mutation

6) An epidemiologic study of sickle cell anemia is performed. The incidence of sickle cell anemia amongst African-Americans in the U.S. is found to be 1 in 625. Based upon this finding, which of the following is the most likely carrier rate for this condition in the U.S. African-American population?

A 2%

B 8%

C 25%

D 33%

E 50%

7) A baby is born at term to a 23-year-old mother. The baby is normal in size. On newborn physical examination, a single midline cleft lip is noted. There are no other congenital anomalies. There is no family history of cleft lip or other birth defects. The parents want to know what the risk will be for this condition if they decide to have more children. Which of the following is the best estimate to give them for a recurrence risk?

A 1%

B 5%

C 25%

D 50%

E 100%

8) A population-based study of mental disorders is conducted. A mental disorder is found that is characterized by periods of hyperactivity followed by periods of sluggishness and inactivity. This disorder is observed in monozygous twins at a higher rate than for dizygous twins or for the general population. This disorder is most likely to represent an increased risk for which of the following?

A Empirical risk

B Brain malformation

C Concordance

D Threshold of liability

E Environmental influence

9) A clinical study is performed to analyze the effectiveness of measures to prevent skin cancer in a population. The use of sunscreen when outdoors for long periods of bright sun is shown to reduce the risk for skin cancer. This risk reduction is mostly likely to occur when which of the following cellular genetic abnormalities events happens less frequently?

A Non-disjunctional event

B Point mutation in a gene

C Pyrimidine dimer formation

D Chromosomal translocation

E Tumor suppressor gene activation activity

10) In a population donating blood for transfusion therapy, the distribution of blood types is found to be as follows:
A - 41%

B - 22%

O - 36%

AB - 1%

Based upon these results, most persons who are blood group A:

A Are homozygotes

B Demonstrate codominance

C Represent the most common allele in U.S. causasians

D Will have more children with the O type

E Have a coagulopathy

11) A rare inborn error of metabolism involving an enzyme occurs in two males in the second generation and two females in the fourth generation of a family founded by two immigrants from the same country. Which of the following genetic mechanisms best explains why this could happen?

A Consanguinity

B Incomplete penetrance

C Spontaneous new mutation

D Uniparental disomy

E X-linked inheritance

12) A disorder is seen more frequently in the males of a particular family, with increasing incidence in successive generations. Some males are carriers. This pattern is most characteristic for which of the following inherited diseases?

A Familial hypercholesterolemia

B Fragile X syndrome

C Hemophilia A

D Marfan syndrome

E Prader-Willi syndrome

13) A 43-year-old man develops the gradual onset of a debilitating movement disorder with awkward twisting and flailing movements of his extremities over the past 3 years. His mental function diminishes as well. MR imaging of his brain shows ex vacuo ventricular dilation with decreased size of the caudate nuclei. What is the most likely recurrence risk for inheritance of this disorder in his children?

A 1%

B 5%

C 25%

D 50%

E 100%

14) A cell from a buccal smear from an adult woman is observed to have two Barr bodies. On physical examination she has no abnormal findings noted. Which of the following is her karyotype most likely to be?

A 46, XX

B 47, XXY

C 47, XXX

D 69, XXX

E 92, XXXX

15) A 29-year-old woman gives birth to a term infant. The baby is noted to have anomalies involving limbs, skull, and heart. Which of the following types of genetic alterations is most likely to lead to this appearance?

A Activation of an oncogene

B Extra Y chromosome

C Loss of an autosome

D Mutation in a gene coding for an enzyme

E Mutation in a transcriptional gene

24) A 23-year-old woman has been pregnant 4 times in the past 5 years. Two of the pregnancies ended in stillbirth. One of these stillbirths received a chromosome analysis, and the karyotype showed a 45, XX, -14 pattern. Of the three liveborn children, two have a 47, XX, +21 and 47, XY, +21 karyotype respectively. The third has a 46, XX karyotype. Which of the following genetic mechanisms is most likely to lead to these findings?

A Germline mosaicism

B Imprinting

C Maternal Robertsonian translocation

D Non-disjunctional event

E Uniparental disomy


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