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MCAT Question A Day - 3/2/14 - Answer!

Point mutations are changes in a single DNA nucleotide base pair. An addition results in an extra base pair, while a deletion results in an omitted base pair along the DNA molecule. In contrast, a substitution results in an incorrect bas pair replacing the correct one. Which point mutations have the highest probability of causing drastic results?

A.  Substitutions
B.  Deletions
C.  Additions and deletions
D.  All three have equal chances of causing drastic results

The correct answer is (C). Substitutions affect only one codon, and as a result, only one amino acid. Both additions and deletions affect the codons in which they occur, and every codon thereafter (frameshift mutations).

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