Mutation is the change in sequence of nucleotide of DNA.
- Change in sequence of nucleotide brings sudden change in morphological characteristics of an organism. If such change are heritable, then it is called as mutation.
- So, mutation is defined as any heritable change in the sequence of nucleotide of DNA.
Organism with mutation is called mutant while the organism without mutation is
Types of Mutation:
A substitution is a mutation in which there is an exchange between two bases (i.e. a change in a single “chemical letter” such as switching a T to a C). Such a substitution could change a codon to one that encodes a different amino acid and cause a change in the protein produced. Sometimes substitutions may not effects the protein structure, such mutations are called silent mutations and sometimes they may change an amino-acid-coding codon to a single “stop” codon and cause an incomplete protein. This can seriously affect the protein structure which may completely change the organism.
Example of Substitution Mutation: Sickle Cell Anaemia is caused by substitution mutation, where in codon (GAG mutates to –> GTG) and leads to (Glu –> Val) change.
Insertions are mutations in which extra base pairs are inserted into a new place in the DNA. The number of base pairs inserted can range from one to thousands!
Example of Insertion Mutation:Huntington’s disease and the fragile X syndrome are examples of insertion mutation wherein trinucleotide repeats are inserted into the DNA sequence leading to these diseases.
Deletions are mutations in which a section of DNA is lost, or deleted. The number of base pairs deleted can again range from one to thousands!
Insertions and Deletion mutations are often together dubbed as INDELS.
Example of Deletion Mutation: 22q11.2 deletion syndrome is caused by the deletion of some bases of chromosome 22. This disease is characterized by cleft palate, heart defects, autoimmune disorders etc.
Protein-coding DNA is divided into codons which are three bases long, insertions and deletions in these codons can completely change a gene so its message cannot be decoded correctly. Such mutations are called frameshift mutations. For example, consider the sentence, “The cat ate her rat.” Each word represents a codon. If we delete the first letter and read the sentence in the same way, it doesn’t make sense. Similarly if the codons become jumbled up, they would no longer make any sense, in such frameshifts, a similar error occurs at the DNA level, where the codons cannot be parsed correctly. This usually gives rise to truncated proteins that are as useless as “rca tet hce tee” is uninformative
Examples of Frameshif Mutation: Tay-Sachs Disease, Cancers of many types, Crohn’s Disease, cystic fibrosis have been associated with Frameshift Mutation.