A mutation that results in the addition of one or more nucleotides to a gene is called what?

A mutation that results in the addition of one or more nucleotides to a gene is known as an insertion mutation. This type of mutation can alter the reading frame of the gene, which can significantly impact how the gene is expressed and the resulting protein's structure and function. Insertions can occur due to various mechanisms, such as template slippage during DNA replication or transposable elements inserting themselves into the DNA sequence.

In the context of genetic mutations, it's also important to note the implications of such changes. An insertion mutation can lead to frameshift mutations if the number of nucleotides added is not a multiple of three. This happens because the grouping of codons that dictate the translation into proteins is shifted, potentially leading to the production of a completely different protein.

The other types of mutations listed do not involve the addition of nucleotides: a base substitution mutation replaces one nucleotide with another, a deletion mutation removes nucleotides, and a nonsense mutation creates a premature stop codon. Each of these types affects the genetic sequence differently than an insertion.