Sunday, 13 December 2015

Common Genetics Multiple Choice Questions And Answers

31- Two strains of Escherichia coli are isolated and both are resistant to ampicillin. Strain A retains its resistance to amplicillin when grown form multiple generations in the absence of ampicillin. However strain B loses its resistance when grown in the absence of ampicillin. Which of the following best explains the loss of antibiotic resistance in strain B?
1) Changes in the bacterial DNA gyrase
2) Downregulation of the resistance gene
3) Loss of a plasmid containing the resistance gene
4) Mutations in the resistance gene
5) Transposition of another sequence into the resistance gene

32- Which of the following is true regarding chromosomes?
1) Down's syndrome is most commonly due to an extra copy of chromosome 21 inherited from the father.
2) A Fetus with triploidy will have 47 chromosomes
3) Heterochromatin is mostly composed of active genes
4) The normal human karyotype consists of 22 pairs of autosomes
5) Telomeres provide the point of attachment to the mitotic spindle

33- A 36-year-old man attends clinic with his wife after failing to conceive after 10 years of marriage. Examination reveals that he his tall, thin and has bilateral gynaecomastia. Investigations show high levels of urinary gonadotrophins. What is the most likely diagnosis?
1) Andropause
2) Gaucher's disease
3) Kleinfelter's syndrome
4) Marfan syndrome
5) Noonan's syndrome
Gaucher's and Marfan syndrome do not present with infertility. Noonan's is associated with short stature. Kleinfelter's is a sex chromosome disorder affecting
1:400 - 1:600 male births typically with 47 XXY, XXXYY or XXYY. Andropause is the term for the gradual decrease in serum testosterone concentration with age, but
does not occur, usually, until after the age of 50.

34- Which one of the following statements is correct?
1) adult polycystic renal disease is inherited as an autosomal recessive trait
2) reflux nephropathy is inherited as an autosomal recessive trait
3) nephrogenic diabetes insipidus is inherited as an autosomal dominant trait
4) Alport's syndrome affects females more severely than males
5) medullary sponge kidney is typically not inherited but is a congenital condition.
PKD is usually autosomal dominant although the infantile form is autosomal recessive. Nephrogenic DI is usually X-linked. Features of Alport syndrome (hereditary nepritis, haematuria, progressive renal failure and high-frequency nerve deafness) are usually more marked in in males. Neither reflux nephropathy
nor medullary sponge kidneys are hereditary conditions.

35- A 22-year-old lady is affected by an inherited disorder. She has two brothers who are unaffected. She has two sisters both are affected. Her father is affected but not her mother. What is the mode of inheritance?
1) Autosomal Dominant
2) Autosomal Recessive
3) Mitochondrial
4) X-linked Dominant
5) X-linked Recessive

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