Section: Biological and Biochemical Foundations of Living Systems

20) 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?

1. 5’ – GCATCCTCATG – 3’
2. 5’ – TGATCCCAG – 3’
3. 5’ – GGTCCTCATC – 3’
4. 5’ – GGATCCATG – 3’

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).