Mutation
Definition
A mutation is a permanent change in the DNA sequence of an organism. Mutations can occur spontaneously or be induced by mutagens (radiation, chemicals). They can be beneficial, harmful, or neutral. Mutations are the ultimate source of genetic variation and drive evolution.
Key Points for NEET
- 1Can be point mutations or chromosomal mutations
- 2Point mutations: substitution, insertion, deletion
- 3Frameshift mutations change reading frame
- 4Silent mutations don't change amino acid
- 5Can be germline (heritable) or somatic (non-heritable)
Example
Sickle cell anemia caused by a single nucleotide change in hemoglobin gene
Asked in NEET
Common Mistakes to Avoid
- ✗Thinking all mutations are harmful — many are neutral, and some are beneficial (e.g., antibiotic resistance in bacteria)
- ✗Confusing point mutations (single nucleotide) with chromosomal mutations (large-scale rearrangements)
- ✗Forgetting that silent mutations change the codon but NOT the amino acid due to degeneracy of genetic code
Quick Revision Notes
- ⚡Point mutations: Substitution (transition/transversion), Insertion, Deletion
- ⚡Frameshift: insertion or deletion shifts reading frame — usually more severe than substitution
- ⚡Sickle cell: GAG→GUG (Glu→Val at position 6 of β-globin) — classic NEET example
- ⚡Mutagens: UV light (thymine dimers), X-rays (chromosomal breaks), chemicals (base analogs like 5-BU)
Related Terms
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More Genetics Definitions
DNA Replication
DNA replication is the biological process by which a DNA molecule makes an identical copy of itself. This semiconservative process ensures that genetic information is accurately transmitted from parent to daughter cells during cell division. Key enzymes include DNA polymerase, helicase, and ligase.
Transcription
Transcription is the first step of gene expression, where a segment of DNA is copied into RNA (specifically mRNA) by the enzyme RNA polymerase. This process occurs in the nucleus in eukaryotes and transfers genetic information from DNA to messenger RNA, which then carries the code to ribosomes for protein synthesis.
Translation
Translation is the process by which ribosomes decode the mRNA sequence into a polypeptide chain (protein). It involves transfer RNA (tRNA) molecules that bring specific amino acids to the ribosome, where they are joined together in the order specified by the mRNA codons. This occurs in the cytoplasm.