Video Transcript
A student said, “All mutations have harmful effects.” Is this true or false?
A mutation is a change in the genetic sequence of an organism. When answering this question, it’s important to consider both the type and the location of the mutation. It’s also necessary to recall the central dogma of biology. Which states that DNA is transcribed into RNA and that RNA is translated into a series of amino acids, which are eventually folded to form a functional protein.
We’ll use this simple four-codon sequence of DNA to illustrate the different types of mutations. Firstly, we transcribe the DNA into RNA. During transcription, the base T for thymine is replaced by U for uracil. After translation, our amino acid sequence reads methionine, isoleucine, serine, stop.
Now, let’s look at that same DNA sequence and imagine that it’s undergone a mutation in which one base is replaced with another. This is called a substitution mutation. After transcription, we notice a corresponding change in the RNA sequence, which leads to a change in the amino acid sequence. Here, we can see isoleucine has been changed to asparagine. A change in the amino acid sequence can lead to a change in the functionality of the protein, which is potentially harmful for the organism.
Let’s examine two more examples of different types of mutations. Here’s an example of an insertion mutation. The entire DNA sequence is the same as the original, except an extra base has been added, which slightly shifts the rest of the sequence. This causes a similar change in the RNA sequence and a significant change in the amino acid sequence, which means that this type of mutation is also potentially harmful.
The last type of mutation we’ll look at is a silent mutation. In this type of mutation, one base is replaced by another, which causes a corresponding change in the RNA sequence, but absolutely no change in the amino acid sequence. Since the amino acid and, thus, the protein is unaffected, this type of mutation will not have harmful effects on the organism.
When discussing mutations, it’s also important to consider the location of the mutation. In eukaryotic DNA, some sections contain genes, while other sections are noncoding or not used. While a mutation in a coding section of DNA has the potential to be harmful, mutations in noncoding sections of DNA are much less likely to have a harmful effect.
Since there are some types of mutations that have no effects at all, when the student said, “All mutations have harmful effects,” they were incorrect and this statement is false.
