Permanent alterations in DNA that affect the nucleotide sequence of one or more genes are called mutations.

Mutations are changes in the genetic code of an organism. They can be caused by a variety of factors, including:

* Errors during DNA replication: The process of copying DNA isn't perfect, and occasional mistakes can lead to mutations.

* Exposure to mutagens: Certain chemicals, radiation, and viruses can damage DNA and cause mutations.

* Insertions or deletions: Adding or removing nucleotides from the DNA sequence can alter the gene's function.

* Substitutions: One nucleotide can be replaced by another, which can change the amino acid sequence of a protein.

The effects of mutations can vary widely:

* Silent mutations: Some mutations don't have any noticeable effect on the protein produced.

* Missense mutations: These mutations change the amino acid sequence of a protein, which can affect its function.

* Nonsense mutations: These mutations introduce a premature stop codon, resulting in a truncated protein.

* Frameshift mutations: Insertions or deletions that shift the reading frame of the DNA sequence, altering the amino acid sequence of the entire protein.

Mutations are a fundamental source of genetic variation and can be beneficial, harmful, or neutral. They play a crucial role in evolution, allowing organisms to adapt to changing environments.