mutations

Mutations are heritable changes in the genetic material of organisms. In organisms with DNA genomes, a mutation refers to a change in the nucleotide sequence of DNA; in RNA viruses, similar changes occur in RNA. Mutations can also involve larger structural changes to chromosomes or shifts in copy number. They arise spontaneously through errors in DNA replication or DNA repair, and can also be induced by environmental factors known as mutagens, such as ultraviolet light, certain chemicals, or radiation.

Types: Point mutations include substitutions of a single nucleotide; these can be silent (no change in amino acid), missense (different amino acid), or nonsense (introducing a stop codon). Insertions and deletions can alter reading frames (frameshift) or remove/add amino acids without shifting the frame. Larger-scale mutations include duplications, deletions, inversions, and translocations that affect chromosome structure; copy-number variations change the number of copies of a genomic region. Aneuploidy refers to abnormal chromosome numbers.

Consequences: Most mutations are neutral, some deleterious, and a minority beneficial. In somatic cells, mutations can contribute to diseases such as cancer; in germ cells, they can be inherited and influence evolution. Mutations introduce genetic variation that selection, drift, and recombination act upon.

Repair and rates: Organisms possess DNA repair pathways that reduce the mutation rate, including mismatch repair and base/excision repair. The mutation rate depends on genome size, replication fidelity, repair efficiency, and environmental exposure. Detection techniques include sequencing, genotyping arrays, and cytogenetic analyses, used to study mutation spectra and inheritance patterns.