Mutations are permanent changes in the DNA sequence of an organism. They can occur naturally during DNA replication or be induced by external factors such as radiation, chemicals, or viruses. Mutations can affect a single nucleotide (point mutations), large segments of a chromosome (chromosomal mutations), or even the number of chromosomes (aneuploidy).
Types of Mutations
Point Mutations: Changes in a single nucleotide base.
Substitution: One base is replaced by another (e.g., A → G).
Silent: No change in the amino acid sequence.
Missense: Changes one amino acid in a protein.
Nonsense: Creates a premature stop codon.
Insertion or Deletion: Addition or removal of one or more nucleotides, possibly causing a frameshift.
Chromosomal Mutations:
Deletion: Loss of a segment of a chromosome.
Duplication: Repetition of a chromosome segment.
Inversion: A chromosome segment is reversed.
Translocation: A segment of one chromosome attaches to another.
Aneuploidy:
Abnormal number of chromosomes (e.g., Down syndrome due to trisomy 21).
Consequences of Mutations
Neutral Effects:
Many mutations are silent or occur in non-coding regions, having no observable effect on the organism.
Harmful Effects:
Loss of Function: Mutations in essential genes can impair protein function, leading to diseases like cystic fibrosis or sickle cell anemia.
Cancer: Accumulated mutations in genes controlling cell division (e.g., tumor suppressor genes) can lead to uncontrolled growth.
Developmental Disorders: Large-scale chromosomal mutations often disrupt normal development.
Beneficial Effects:
Rarely, mutations may provide advantageous traits (e.g., antibiotic resistance in bacteria, enhanced fitness in specific environments), driving evolution.
Hereditary vs. Somatic Effects:
Germline Mutations: Passed to offspring, affecting future generations.
Somatic Mutations: Occur in body cells and affect only the individual (e.g., mutations in cancerous tissues).