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MCAT Biology Questions — DNA Mutation and Deletion

  • by Kerry Goldstein
  • Jan 21, 2015
  • MCAT Biology, MCAT Blog, MCAT Question of the Day

A segment of DNA from a lab mouse is determined to be 5’ – GGATCCTCATG – 3’. Which of the following DNA segments would be the result of this original DNA sequence experiencing both a point mutation and a deletion?

A) 5’ – GCATCCTCATG – 3’

B) 5’ – TGATCCCAG – 3’

C) 5’ – GGTCCTCATC – 3’

D) 5’ – GGATCCATG – 3’

 

 

Explanation

A point mutation is one in which a single DNA base has be replaced by another and a deletion in one in which a single DNA base has been deleted. The question asks us to look for an answer choice that has had both a point mutation and a deletion. Only choice (C) matches these requirements.

A) 5’ – GCATCCTCATG – 3’

B) 5’ – TGATCCCAG – 3’

C) 5’ – GGTCCTCATC – 3’

D) 5’ – GGATCCATG – 3’

 

A, D: Neither (A) nor (D) has had any deletions at all – the length of the DNA chain is unchanged.

B: Two deletions have occurred as well as a point mutation. Both the 7th and 10th nucleotide are missing (both T).

 

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