Block 7 Trinuc Repeat X Inact & Duchene MCQ's

21 Questions | By Chachelly | Updated: Mar 21, 2022 | Attempts: 512

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Block 7 Trinuc Repeat X Inact & Duchene MCQ

Questions and Answers

1.

A single Barr body is typical for
- A.
  
  A) a triple-X superfemale
- B.
  
  B) an infertile patient with Klinefelter syndrome
- C.
  
  C) A death row inmate with XYY "murderer chromosome"
- D.
  
  A phenotypic female with androgen insensitivity syndrome ("testicular feminization")
- E.
  
  A female with Turner syndrome
2.

A boy with Duchenne muscular dystrophy (DMD) was born to parents with no family history of the disease. The most likely explanation for this occurrence is
- A.
  
  A CGG expansion that resulted in the disruption of the promoter of the dystrophin gene
- B.
  
  Infidelity
- C.
  
  A point mutation in the dystrophin gene
- D.
  
  A recombination event in the dystrophin gene that gave rise to a frameshift mutation leading to an untranslatable mRNA
- E.
  
  A translocation that resulted in the disruption of the dystrophin gene
3.

A family is referred to a genetic specialist because of mild mental retardation in several of the school-age children. Laboratory evaluation demonstrates a specific chromosomal breakage site in metaphase studies of lymphocytes cultured with methotrexate. Which of the following chromosomes is most likely to be specifically affected?
- A.
  
  X
- B.
  
  Y
- C.
  
  13
- D.
  
  18
- E.
  
  21
4.

A 43-year-old man is brought to the general medicine clinic by his wife. She states that his memory has progressively deteriorated over the last several years, and that his personality has been changing. On examination, the physician notes abnormal, writhing movements of the man's limbs and hyperreactive patellar reflexes. An MRI of the head reveals a loss of volume in the neostriatum and cortex. A family history reveals that similar symptoms occurred in several members of the patient's family. Which of the following genetic mechanisms has been implicated in this disorder?
- A.
  
  Expanded trinucleotide tandem repeat
- B.
  
  Genomic imprinting
- C.
  
  Large deletion in one gene
- D.
  
  Single amino acid substitution
- E.
  
  Translocation
5.

A 3 year-old boy is brought to a physician because the mother notices that the child is engaging in less active play and tires easily. During physical examination, the pediatrician notices that the child's thighs are larger than normal for age and that the child cannot stand up without using his arms to help. Further studies demonstrate a defective dystrophin gene in the boy. Which of the following people in the child's family is most likely to also have this disease?
- A.
  
  Father
- B.
  
  Father's brother
- C.
  
  Mother
- D.
  
  Mother's brother
- E.
  
  Sister
6.

A 13-year-old boy is brought to a rural clinic because of poor school performance. His parents state that he did not begin talking until after three years of age, and still does not use language as effectively as his sister, who is 6-years-old. A careful family history reveals that a maternal grandfather was mildly retarded. The mother has two sisters, both of whom are apparently normal, but the mother admits that she did not do well in school, and dropped out at the age of 16. Physical examination of the child reveals large ears, a long, narrow face, and large testes. Which of the following genetic mechanisms most likely accounts for the observed findings in the son?
- A.
  
  Trisomy 18
- B.
  
  Genomic imprinting
- C.
  
  Robertsonian translocation
- D.
  
  Trisomy 13
- E.
  
  Expanded trinucleotide repeat
7.

Although II-3 tested negative for the mutation seen in her brother, the physician is concerned regarding the persistent CK level of II-3. The pregnancy was tested again and showed a deletion of exon 45-48 considered consistent with being affected with DMD. The most likely explanation of the results is?
- A.
  
  Non maternity
- B.
  
  Non paternity
- C.
  
  Somatic mosaicism of III-2
- D.
  
  Laboratory error in the testing of II-3
- E.
  
  De Novo mutation in III-2
8.

Triplet repeat expansions (CGG) in Fragile X syndrome interferes by?
- A.
  
  Decreasing mRNA synthesis
- B.
  
  Increasing mRNA synthesis
- C.
  
  Creating splicing defect
- D.
  
  Gain of function mutation
- E.
  
  Dominant negative mutation
9.

The following pedigree shows a family segregating for Duchenne Muscular Dystrophy (DMD). Individual II-1 was found to have a deletion of exons-45-48 of the dystrophin gene. Individual 11-3 is currently pregnant with a boy. She shows an elevated CK but she tested negative for this mutation. The risk for the pregnancy 111-2 to have DMD is closest to?
- A.
  
  0%
- B.
  
  10%
- C.
  
  50%
- D.
  
  75%
- E.
  
  100%
10.

A dominantly inherited trait affects a child and his grandmother, but neither parent. This best illustrates which of the following principles?
- A.
  
  Variable expressivity
- B.
  
  New mutation
- C.
  
  Somatic mosaicism
- D.
  
  Non-penetrance
11.

Characteristic of Fragile X syndrome
- A.
  
  The gene is located at the end of the short arm of the X and the Y chromosomes
- B.
  
  Males and females are affected equally
- C.
  
  The mutation involves expansion of a triplet repeat and anticipation occurs when transmitted by a male
- D.
  
  The mutation involves expansion of a triplet repeat and anticipation occurs when transmitted by a female
- E.
  
  The mutation exerts a gain of function effect
12.

Evidence that Huntington disease is due to a "gain of function" mutation in the gene which codes for the huntington protein, comes from:
- A.
  
  The fact that disease-causing mutations in this gene involve expansions rather than contractions of a trinucleotide repeat.
- B.
  
  The fact that there is a correlation between numbers of trinucleotide repeats in this gene and the age of onset of Huntington disease
- C.
  
  The larger molecular weight protein coded by the mutant gene being inactive
- D.
  
  The finding that a translocation involving a breakpoint in this gene does not lead to Huntington disease
13.

Fragile X syndrome is caused by the dramatic expansion of a CGG sequence in the 5' untranslated region of the FMR1 gene. Which of the following is the consequence of this expansion?
- A.
  
  Too much FMR1 gene product is synthesized
- B.
  
  The expansion causes a frameshift mutation, and the resulting gene product cannot function
- C.
  
  The 5' untranslated region is hypermethylated when the repeats reach a certain size, leading to the loss of transcription of the gene.
- D.
  
  Expansion of the trinucleotide repeats produces a toxic "gain of function" mutation
- E.
  
  The expansion causes a nonsense mutation and the gene product is not produced
14.

SRY, like other genetic switches, has a DNA-binding domain, consistent with its function during gonadal development as a:
- A.
  
  Receptor
- B.
  
  Transcription factor
- C.
  
  Metabolic enzyme
- D.
  
  Structural protein
15.

The mother of a boy with molecularly proven Duchenne muscular dystrophy has mild weakness and an elevated serum creatine kinase (CK). What most likely accounts for this?
- A.
  
  X-inactivation (Lyonization)
- B.
  
  She has testicular feminization syndrome
- C.
  
  She is 45,X
- D.
  
  She is 47,XXX
- E.
  
  She is 47,XXY
16.

If there is a family history of genetic disorders, knowing the gender of an unborn child can be important because
- A.
  
  Male children are more likely to have autosomal defects show up in their phenotypes
- B.
  
  Female children are more likely to have autosomal defects show up in their phenotypes
- C.
  
  Male children are more likely to have X-linked traits show up in their phenotype
- D.
  
  Answer A and C are correct
17.

An exchange of fragments of chromatids between non-homologous chromosomes may occur during the first meiotic division. This chromosomal structural abnormality is called:
- A.
  
  Deletion
- B.
  
  Inversion
- C.
  
  Nondisjunction
- D.
  
  Segregation
- E.
  
  Translocation
18.

A 4-year-old boy is brought to the physician by his parents because of a 4-month history of difficulty running and frequent falls. His parents report that his calves have been gradually increasing in size during this period. Examination shows diffusely enlarged muscles of the calves and lumbar lordosis. Sensation is intact. He has difficulty arising from a supine position. Which of the following is the most likely diagnosis?
- A.
  
  Duchenne muscular dystrophy
- B.
  
  Juvenile rheumatoid arthritis
- C.
  
  Lumbosacral radiculopathy
- D.
  
  Rhabdomyosarcoma
- E.
  
  Spina bifida
19.

A 28 year-old African American female presents to your OB/GYN clinic to discuss her Risk to be carrier for Duchenne/Becker muscular dystrophy. She is currently 9 weeks pregnant. The patient reports an innocent mummur which was evaluated by a cardiologist and does not require follow-up. She has otherwise normal medical history and normal pregnancy to date. The patient has one healthy 2 year-old daughter who has a history of recurrent ear infections but otherwise healthy. Patient reports having a 25 year-old sister who is in good health and does not have yet children. The patient has a maternal uncle who died at the age of 16, due to a form of muscular dystrophy with progressive, severe “muscle weakness” and respiratory difficulty. The patient also reports that her maternal aunt has a 37 year-old healthy daughter, a 34 year-old healthy son and a son who died at the age of 18. This cousin to your patient was considered by the family to have the same disease as the uncle. The cousin was unable to walk, and died for cardiac and respiratory complications. Your patient’s partner does not have a family history of any form of muscular dystrophy and the couple denies any consanguinity What is the most likely diagnosis for your patient’s family?
- A.
  
  Down syndrome
- B.
  
  Duchenne Muscular dystrophy
- C.
  
  Myotonic Dystrophy
- D.
  
  Huntinton disease
20.

A 28 year-old African American female presents to your OB/GYN clinic to discuss her Risk to be carrier for Duchenne/Becker muscular dystrophy. She is currently 9 weeks pregnant. The patient reports an innocent mummur which was evaluated by a cardiologist and does not require follow-up. She has otherwise normal medical history and normal pregnancy to date. The patient has one healthy 2 year-old daughter who has a history of recurrent ear infections but otherwise healthy. Patient reports having a 25 year-old sister who is in good health and does not have yet children. The patient has a maternal uncle who died at the age of 16, due to a form of muscular dystrophy with progressive, severe “muscle weakness” and respiratory difficulty. The patient also reports that her maternal aunt has a 37 year-old healthy daughter, a 34 year-old healthy son and a son who died at the age of 18. This cousin to your patient was considered by the family to have the same disease as the uncle. The cousin was unable to walk, and died for cardiac and respiratory complications. Your patient’s partner does not have a family history of any form of muscular dystrophy and the couple denies any consanguinity Before any testing is performed what is your patient’s risk to be carrier for this condition?
- A.
  
  100%
- B.
  
  50%
- C.
  
  25%
- D.
  
  0%
21.

A 28 year-old African American female presents to your OB/GYN clinic to discuss her Risk to be carrier for Duchenne/Becker muscular dystrophy. She is currently 9 weeks pregnant. The patient reports an innocent mummur which was evaluated by a cardiologist and does not require follow-up. She has otherwise normal medical history and normal pregnancy to date. The patient has one healthy 2 year-old daughter who has a history of recurrent ear infections but otherwise healthy. Patient reports having a 25 year-old sister who is in good health and does not have yet children. The patient has a maternal uncle who died at the age of 16, due to a form of muscular dystrophy with progressive, severe “muscle weakness” and respiratory difficulty. The patient also reports that her maternal aunt has a 37 year-old healthy daughter, a 34 year-old healthy son and a son who died at the age of 18. This cousin to your patient was considered by the family to have the same disease as the uncle. The cousin was unable to walk, and died for cardiac and respiratory complications. Your patient’s partner does not have a family history of any form of muscular dystrophy and the couple denies any consanguinity Based on your patient’s risk to be a carrier, what is her chance that the pregnancy could be affected ?
- A.
  
  100%
- B.
  
  50%
- C.
  
  25%
- D.
  
  6%
- E.
  
  12.5%
- F.
  
  0%