A mutation is a permanent change in the DNA sequence of an organism’s genome that can occur spontaneously or be induced by environmental factors.
Explanation
Mutations arise when errors during DNA replication are not corrected or when chemical, physical or biological agents damage the genome. Changes may involve single nucleotides, small stretches of bases or large chromosomal segments. Point mutations alter one base pair; they can be transitions or transversions and may result in silent, missense or nonsense substitutions depending on whether they change an amino acid or create a stop codon. Insertions and deletions of nucleotides can shift the reading frame of a coding sequence, often leading to premature termination and nonfunctional proteins. Larger structural mutations include duplications, inversions and translocations. Endogenous processes such as oxidative stress and spontaneous deamination, as well as exogenous mutagens like ultraviolet light, ionizing radiation and chemicals, contribute to mutation. Cells possess repair mechanisms that correct many lesions, but some alterations escape repair and become fixed in the genome. While many mutations are neutral, some confer advantage or cause disease. They are the raw material of evolution and diversity.
Types and Effects
The single base substitution in the β-globin gene that converts glutamic acid to valine causes sickle cell disease by altering haemoglobin structure. A three-base deletion in the CFTR gene resulting in loss of phenylalanine (ΔF508) is the most common cause of cystic fibrosis. Point mutations in bacterial ribosomal genes confer resistance to antibiotics such as streptomycin and rifampin. Frameshift mutations introduced by insertions or deletions can truncate proteins, as seen in some BRCA1 mutations associated with breast cancer. Not all mutations are harmful; a regulatory mutation in the lactase gene allows continued lactose digestion in many adult humans, and certain mutations in the CCR5 gene confer resistance to HIV. Understanding mutation types and their effects guides research in genetics, medicine and evolution.
Mutations are central to heredity and diversity; they drive adaptation but can also lead to genetic disorders and cancer. The balance between DNA damage, repair and selection shapes the genetic landscape of populations.
Related Terms: DNA, Mutagen, Polymorphism, Gene, Genome