A mutation is a change in the DNA sequence that can cause disease, affect symmetry, or drive evolutionary processes.A mutation is a permanent change in the nucleotide sequence (the building blocks of DNA) of DNA, arising from replication errors (DNA duplication), recombination (exchange of segments between chromosomes), or under the influence of mutagens (factors that cause mutations). Point mutations affect a single base pair; their types: substitution (missense — amino acid substitution, nonsense — stop codon appearance), insertion or deletion, often leading to a reading frame shift (alteration of codon grouping). Chromosomal mutations are larger rearrangements: deletions (loss of segments), duplications (doublings), inversions (180° rotation), translocations (relocations). Genomic mutations change the number of chromosomes (aneuploidy — abnormal number, polyploidy — multiplication of the entire set). Mutations can be somatic (in non-reproductive cells, not transmitted) or germinal (in reproductive cells, inherited). Most mutations are neutral or harmful, but in rare cases increase fitness, becoming material for natural selection.
The concept of mutations as discrete changes dates back to Hugo de Vries, who in 1901–1903 described them in evening primrose, using the term "mutation" to denote sudden heritable deviations. Thomas Morgan and his school, working with fruit flies in the 1910s, established the connection between mutations and chromosomes. In 1927, Hermann Muller experimentally proved the mutagenic effect of X-rays, laying the foundations of radiation genetics. In the mid-20th century, the discovery of the structure of DNA allowed a transition to molecular understanding of mutations.
At the molecular level, mutations arise as a result of chemical changes in nucleotides or errors in template synthesis. For example, deamination of cytosine converts it to uracil, which during replication is read as thymine, replacing a C-G pair with T-A. Sources of spontaneous mutations include tautomeric shifts of bases, leading to mispairings during replication. Induced mutations occur after DNA attack by exogenous agents. If the repair system fails, the change becomes fixed in the next replication cycle. Consequences depend on the type of mutation and its location: mutations in promoter regions alter gene expression levels; nonsense mutations truncate the protein; mutations in splice sites disrupt intron removal; epigenetic changes do not affect the DNA sequence but can be heritable. The evolutionary significance of mutations is as the primary source of genetic variation for natural selection.
Mutations underlie evolution and the diversity of life, and their study helps understand the causes of cancer and create new plant varieties.
In humans, each germ cell carries on average about 100 new mutations not present in the parents, making us all a bit mutant.







