Final answer:
An insertion mutation occurs when a nucleotide is added to a DNA sequence, leading to a frameshift mutation. The insertion of a single nucleotide is more harmful than the insertion of three nucleotides because it alters the downstream reading frame, potentially resulting in a nonfunctional protein. These changes can have profound effects on an organism's phenotype if not corrected by cellular repair mechanisms.
Step-by-step explanation:
A mutation that results in a nucleotide being inserted into the DNA sequence is known as an insertion mutation. This type of mutation can cause a frameshift mutation, which occurs when one or more nucleotides are added to the DNA sequence. Since the genetic code is read in triplets called codons, adding or deleting nucleotides can disrupt the reading frame. An insertion mutation might lead to the creation of a different set of amino acids during translation, significantly altering the protein that is produced.
When there is an insertion of one nucleotide, it is often more deleterious than the insertion of three nucleotides because the insertion of three nucleotides will add an extra codon without affecting the downstream reading frame. However, a single-nucleotide insertion changes the reading frame from that point onwards, which can result in a completely different and often nonfunctional protein. This alteration is known as a frameshift mutation and can seriously affect the structure and function of proteins, with potentially severe phenotypic consequences.
Mutations can occur during DNA replication if an incorrect nucleotide is inserted into the new strand of DNA. These changes are usually corrected by the cell's repair mechanisms, but if not, they result in a permanent change in the DNA sequence known as a mutation. Therefore, a frameshift mutation due to nucleotide insertion is a potential source of significant genetic variation and can lead to changes in the phenotype of the organism.