What occurs in a deletion mutation?

In a deletion mutation, a segment of the DNA sequence is removed or deleted. This can involve the loss of a single nucleotide or a larger stretch of nucleotides. The impact of this type of mutation can be significant, as it can lead to frameshifts in the reading frame during protein synthesis, potentially resulting in a completely altered protein structure and function. This type of mutation can contribute to various genetic disorders, as the normal sequence is disrupted.

The other options describe different types of mutations or changes that do not fit the definition of a deletion mutation. For instance, duplications and additions pertain to the inclusion of extra nucleotides, and an unaltered sequence indicates no mutation at all. Each of these scenarios distinctly contrasts with the essential characteristic of a deletion mutation, which is the loss of genetic material from the sequence.