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Gentics-the most important 10MCQ/Part2
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03.22.06 (2 years ago)
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Q1-In autosomal recessive inheritance:all of the following are true except
a. the rarer the trait the higher the possibility of marriages
within the same family
b. most recessive gene defects cause problem through
failure to produce functional protein
c. both males and females are affected equally severely
d. the chance of a child being affected if both parents are
carriers of a recessive gene is 50%
e. autosomal recessive retinitis pigmentosa is usually more
severe than autosomal dominant retinitis pigmentosa
[/color]Answer D
Each parent has a 50% chance of transmitting the defective allele to a child. Since a child mustreceive a defective allele from both parents to be affected, each child has a 25% chance of being affected.
Q2-Genetic counseling includes all of the following EXCEPT:
A Discussion of available genetic testing
B Recommendation of specific reproductive options
C Assessment of the occurrence or recurrence risk
D Discussion of the impact of the disease on the patient and family
E Discussion of available therapies
ANSWER B
Genetic counseling is a non-directive process that enables the patient to be sufficiently well-informed that they are able to make their own decisions.
Q3-For a given autosomal recessive disease, q = 0.01 (where q is the allele frequency of the mutant allele). Approximately what percentage of the population has two copies of the normal allele?
A 2%
B 19%
C 90%
D 95%
E [snip]%
Answer E
Since the frequency of the mutant allele is 0.01, the frequency of the normal allele is 1 - 0.01, or 0.99. People with 2 copies of the normal allele thus occur at a frequency of (0.99)(0.99) = p2 = 0.[snip] = [snip]%.
Q4-[color=darkblue]A chromosomal analysis is obtained on a young woman with mild signs of Turner syndrome and reveals a 46,XX/45,X karyotype. Nondisjunction is most likely to have occurred in:[/color]
A maternal meiosis I
B maternal meiosis II
C paternal meiosis I
D paternal meiosis II
E mitosis after fertilization
Answer E
Since there is a cell line in this young woman that has a complete chromosome complement (46,XX) she must have received the appropriate amount of maternal and paternal genetic information at the time of fertilization. The loss would have occurred post-fertilization to generate the 45,X cell line. See p.184 in the book.
Q5-Which is true of newborn screening tests for genetic diseases? Newborns are typically screened for genetic diseases:
A which are irreversible or untreatable disorders.
B which are treatable and/or preventable.
C which are fatal by one year of age.
D when a first or second degree relative is known to be affected.
E Newborns are screened for all known genetic diseases.
Answer B
Newborns are screened for genetics diseases that are treatable and/or preventable. There is no point to instituting a costly screening program for diseases that cannot be treated.
Q6-You see a previously healthy 3-day-old male infant who is very lethargic, vomiting, and had a seizure. Which of the laboratory tests would be most appropriate to obtain initially to confirm your suspicions?
A a 24 hour urine homogentisic acid level
B ornithine transcarbamylase gene sequence
C plasma phenylalanine and tyrosine levels
D just a plasma phenylalanine level
E serum ammonia level
Answer E
In OTC deficiency, an X-linked disorder, a deficiency of the enzyme ornithine transcarbamylase affects ammonium metabolism and leads to high level excretion of orotic acid in the urine. Affected males are usually delivered after a full-term gestation and appear normal at birth. They become symptomatic after they start to ingest protein, resulting in the clinical features outlined in the question.
Q8-Alkaptonuria is caused by a deficiency of:
A phenylalanine hydroxylase
B homogentisic acid
C homogentisic acid oxidase
D normal colored urine
E phenylalanine oxidase
Answer C
In individuals affected with alkaptonuria, there is a build-up of homogentisic acid because homogentisic acid oxidase is unable to metabolize this protein to maleylacetoacetic acid. This enzymatic step is part of the pathway involved in the catabolism of phenylalanine and tyrosine to fumaric acid and acetoacetic acid. See Fig. 7.2 in the book for the steps in this pathway.
Q9-A liver transplant may be effective in treating all of the following disorders except:
A severe familial hypercholesterolemia
B ornithine transcarbamylase (OTC) deficiency
C a-1 antitrypsin deficiency
D glucose-6-phosphate dehydrogenase (G6PD) deficiency
Answer D
G6PD deficiency results in hemolytic anemia secondary to a decreased stability of G6PD protein and inability to synthesize mature RBCs (under conditions of oxidative stress). A liver transplant won't be particularly useful for these individuals
Q10-Which of the following human diseases is least likely to be caused by aneuploidy?
A Fragile X syndrome
B Down syndrome
C Turner syndrome
D Klinefelter syndrome
Answer A
Aneuploidy is when the chromosome number is not an exact multiple of the haploid number. Down syndrome (trisomy 21), Turner syndrome (45, X), and Klinefelter syndrome (47, XXY) are all examples of aneuploidy. In contrast, Fragile X syndrome is characterized by expansion of a CGG triplet repeat in the first exon of the FMR-1 gene on the long arm of the X chromosome, with the total chromosome number not being affected (i.e. still euploid).
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