Genetic Mutation
A genetic mutation is a permanent alteration in the nucleotide sequence of an organism's DNA, which may affect one or more genes. Mutations can arise spontaneously during DNA replication, or be induced by mutagens such as radiation, chemicals, or viruses. While many mutations are neutral or harmful, some confer advantages that can be selected for during evolution, making mutations the ultimate source of genetic variation in populations.
Types of Genetic Mutations and Their Effects
| Mutation Type | Description | Example | Effect on Protein |
|---|---|---|---|
| Point mutation (substitution) | Single nucleotide change | Sickle cell: GAG → GTG | Amino acid change (Glu → Val) |
| Insertion | One or more nucleotides added | Frame-shift insertion | Frame shift, altered protein |
| Deletion | One or more nucleotides removed | Cystic fibrosis (ΔF508) | Frame shift or missing residue |
| Nonsense mutation | Creates a premature stop codon | UAG or UAA introduced early | Truncated, non-functional protein |
| Silent mutation | No change in amino acid | Synonymous codon change | No change in protein |
| Chromosomal mutation | Large-scale chromosome change | Down syndrome (trisomy 21) | Major developmental effects |
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Related Terms
Genetic Disorder
A genetic disorder is a disease or condition caused by an abnormality in an individual's genome, which may involve a mutation in a single gene (monogenic), multiple genes (polygenic/multifactorial), or chromosomal abnormalities. Genetic disorders can be inherited from parents (hereditary) or arise as new mutations (de novo). They range widely in severity — from manageable conditions like colour blindness to life-threatening diseases like Huntington's disease — and understanding their genetic basis is crucial for diagnosis, treatment, and genetic counselling.
Phenotype
The phenotype is the observable set of physical and biochemical characteristics of an organism, resulting from the interaction of its genotype with the environment. It encompasses all visible traits such as eye colour, height, blood type, and behavioural tendencies. Understanding phenotype is fundamental to genetics because it reveals how genetic information is expressed in living organisms.
Recessive Allele
A recessive allele is a version of a gene whose trait is expressed in the phenotype only when two copies of it are present (i.e., in the homozygous state), because it is masked by a dominant allele when paired with one. Recessive alleles are conventionally represented by lowercase letters (e.g., "b" for blue eye colour). Many genetic disorders, such as cystic fibrosis and sickle cell anaemia, are caused by recessive alleles.
From Latin "mutatio" meaning "change" or "alteration", derived from "mutare" (to change). The biological use of the term was popularised by Dutch botanist Hugo de Vries in 1901, who observed large heritable changes in Evening Primrose plants and called them "mutations".