Question Video: Determining Which Mutation Types Cause Frameshift Mutations Biology

Which of the following types of mutations can cause a frame shift in a DNA sequence? [A] Substitution and saturation [B] Insertion and deletion [C] Deletion only [D] Substitution only [E] Insertion and inversion


Video Transcript

Which of the following types of mutations can cause a frame shift in a DNA sequence? (A) Substitution and saturation, (B) insertion and deletion, (C) deletion only, (D) substitution only, or (E) insertion and inversion.

DNA is the molecule that carries genetic information in the nuclei of our cells. This information is encoded in a sequence of nitrogenous bases that we can see here as these colored lines. Our cells use the genetic information to synthesize proteins which perform crucial functions in our body. Before this information can be converted into a protein, the cell first converts DNA into a strand of mRNA or messenger RNA. This sequence of mRNA can then be translated into an amino acid sequence to make a protein.

To do this, the cell’s protein synthesizing organelle, the ribosome, reads the strand of mRNA in sets of three nitrogenous bases. Each consecutive set of three bases forms a codon. These codons ensure that a specific corresponding amino acid is brought to the ribosome and incorporated into the correct place in the protein. Sometimes changes can occur to the DNA base sequence, which can affect the amino acid sequence. These changes are called mutations. You can imagine mutations to be like spelling mistakes in a sentence.

There’s three different types of mutations that we’ll look at. In substitution mutations, bases in the DNA sequence are replaced with different bases. In an insertion mutation, one or more bases are added to the DNA sequence, while in a deletion mutation, one or more bases are removed from the DNA sequence. In an insertion or deletion mutation, if the bases are not added or removed in multiples of three, this can cause the reading frame of the resulting mRNA sequence to become skewed.

Let’s take a look at an example of these mutations using a sentence. This sentence is made up of five three-letter words: TOM HAS ONE RED HAT. Let’s imagine that just like the ribosome, we can only read words if they have three letters. If a substitution mutation were to happen at this position, it might read like this. Now the sentence reads TOM HAS ONE RED CAT. This sentence still has five words that make sense, but the meaning has changed from our original sentence.

Now let’s look at an insertion mutation when the letter P is inserted here. The addition of a letter P has changed the reading frame of this sentence entirely. All the letters have been pushed to the right one space. It no longer makes any sense.

Now, let’s look at what happens in a deletion mutation where we remove a letter. Once again, this has caused a shift in the reading frame. All the letters have been pulled one space to the left, and the resulting sentence again doesn’t make any sense. These mutations in which the reading frame changes are called frame shift mutations. As we have seen, insertion and deletion mutations are the ones capable of causing such a change. So of the included possible answer choices, the correct answer is insertion and deletion.

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