Oncology Certified Nurse (OCN) Nursing Practice Test

What type of mutation occurs when one or more bases are added or deleted from the DNA sequence?

1. Missense

2. Frameshift

3. Translocation

4. Aneuploidy

The correct answer is: Frameshift

When one or more bases are added or deleted from the DNA sequence, it results in a frameshift mutation. This type of mutation causes a shift in the reading frame of the genetic code during protein synthesis, altering the entire amino acid sequence downstream of the mutation. As a consequence, the resulting protein may be significantly different, which can lead to loss of function or the production of a nonfunctional protein. This phenomenon occurs because the DNA is read in triplet codons, and adding or removing a base disrupts the grouping of these codons. For instance, if a base is deleted, all codons following that point will be shifted by one nucleotide, changing the expected amino acids that correspond to these new codons. In contrast, other options such as missense mutations involve a change in a single amino acid without a shift in the reading frame, translocation refers to the rearrangement of parts between non-homologous chromosomes, and aneuploidy denotes an abnormal number of chromosomes rather than changes in the DNA sequence itself. Therefore, the correct choice accurately describes the specific outcome of base addition or deletion.