Mutations

Mutation is a sudden change in one or more genes, or in the number or in the structure of chromosomes.

or

Mutation is a phenomenon which results in alteration of DNA sequences and consequently results in changes in the genotype and the phenotype of an organism.

A mutation is any sudden, heritable change in the nucleotide sequence of DNA (or in the structure/number of chromosomes) that alters the genotype and may or may not alter the phenotype of an organism.

Attribution: The term mutation and the Mutation Theory of Evolution were proposed by Hugo de Vries in 1901, based on his experiments with the evening primrose (Oenothera lamarckiana). He argued that new species arise through sudden, large mutations (saltation) rather than gradual Darwinian variation.

1. Spontaneous Mutations

• Occur naturally, without any external influence.​
• Caused by intrinsic replication errors, tautomeric shifts in nitrogenous bases, and spontaneous chemical changes in DNA.​
• Rate: Very low (~1 in 10⁶ to 10⁹ base pairs per replication).​

2. Induced Mutations

• Caused by exposure to external agents called mutagens.​

3. Physical Mutagens

4. Chemical Mutagens

• Mutations are the ultimate source of genetic variation in a population.​
• Along with recombination, mutations provide raw material for natural selection.​
• Example: Antibiotic resistance - pre-existing mutant bacteria with resistance genes survive antibiotic treatment and proliferate, shifting the entire population toward resistance.
• Example: DDT resistance in mosquitoes arises through the same selection of pre-existing mutants.​

• A mutation is a sudden heritable change in DNA sequences that leads to changes in the genotype and phenotype of an organism.
• Loss of DNA segment = deletion; gain of DNA segment = insertion/duplication; both cause chromosomal aberrations, commonly seen in cancer cells.
• Frame-shift mutation - caused by loss or gain of a DNA segment; Point mutation - change in a single base pair (e.g., sickle cell anaemia).
• Physical mutagens that cause mutation include UV radiation, X-rays, alpha, beta and gamma rays; Chemical mutagens include mustard gas, phenol and formalin.
• Mutation is an important source of genetic variation in organisms, alongside recombination.