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Repeated USMLE Questions Step 1- 368



Q- Mitochondria are NOT found in which of the following organisms?

A- Fungi

B- Protozoa

C- Viruses

D- Yeasts

C- Viruses- There is no mitochondria in bacteria or viruses.



Q- Measurement of the content of which one of the following could help to compare the collagen content of several tissues?

A- Cysteine

B- Glycine

C- Hydroxyproline

D- Proline

C- Hydroxyproline- Although collagen is rich in glycine, several tissues also contain significant amounts of glycine. Hydroxyproline is found uniquely in collagen.



Q- Which of the following explains the higher incidence of sickle cell disease in African Americans more than other races?

A- Genetic drift

B- Increased gene flow

B- Increased mutation rate

D- Natural selection

D- Natural selection- Heterozygous carriers are resistant to malarial infection but at the same time they don’t develop sickle cell disease because it is autosomal recessive. There is selective advantage for this mutation elevating its incidence in this population.



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