Mutations & Its Types
A mutation is a change that occurs in the DNA sequence, either due to mistakes when the DNA is copied or as the result of environmental factors such as UV light and cigarette smoke.
Mutations may or may not produce visible changes in the observable characteristics (phenotype) of an organism. Mutations play a part in both normal and abnormal biological processes including evolution, cancer, and the development of the immune system, including junctional diversity. Because mutations are random changes, they are expected to be mostly deleterious, but some may be beneficial in certain environments.
Causes of Mutations
- Mutations can occur during DNA replication
- Mobile DNA elements that move from one location to another also cause mutations
- Byproducts of cellular metabolism
- Free radicals
- Ultraviolet rays from the sun
Types of Mutations
- Substitution: One base is incorrectly added during replication and replaces the pair in the corresponding position on the complementary strand
- Insertion: One or more extra nucleotides are inserted into replicating DNA, often resulting in a frameshift
- Deletion: One or more nucleotides is “skipped” during replication or otherwise excised, often resulting in a frameshift
- Chromosomal mutation
- Inversion: One region of a chromosome is flipped and reinserted
- Deletion at chromosome level: A region of a chromosome is lost, resulting in the absence of all the genes in that area
- Duplication: A region of a chromosome is repeated, resulting in an increase in dosage from the genes in that region
- Translocation: A region from one chromosome is aberrantly attached to another chromosome
- Balanced translocation: when two segments are exchanged, resulting in balanced translocation.
- Reciprocal translocation: Reciprocal translocations are more commonly found in nature. It occurs between two non-homologous chromosomes.
- Robertsonian translocation: Robertsonian translocation occurs between two acrocentric chromosomes.
- Errors introduced during DNA repair
- Induced mutations caused by mutagens
- Frameshift mutation: This type of mutation occurs when the addition or loss of DNA bases changes a gene’s reading frame.
- A repeat expansion is a mutation that increases the number of times that the short DNA sequence is repeated. This type of mutation can cause the resulting protein to function.
- Missense mutation: In this type of mutation the changed codon now corresponds to a different amino acid. As a result an incorrect amino acid is inserted into the protein being synthesized.
- Nonsense mutation: In this type of mutation, instead of tagging an amino acid, the altered codon signals for transcription to stop.
- Silent mutation: A silent mutation is a change in the sequence of nucleotide bases which constitutes DNA, without a subsequent change in the amino acid or the function of the overall protein.
- Inversion: It occurs when some gene sequences inverted and inserted back into the original sequence.
- Forward mutation: Genetic Mutation from wild-type to mutant or evolution of new mutation from wild-type allele is called a forward mutation.
- Ring chromosome mutation: when both ends of a chromosome are fused together, it creates a ring-like structure and so-called a ring chromosome.
- Null Allele: a mutant allele with a lack of function.
- Hypomorphic: mutation in which gene function performance is reduced.
- Hypermorph: mutation in which gene function performance is enhanced.
- Neomorph: a gene that has a novel function due to mutation in its sequence.
- Antimorph: a mutation that changes a gene in such a way that it antagonizes the function of a wild type gene/allele.