Define mutation. Illustrate the types of mutations that can arise by change in chromosome structure.

A mutation is a change in the DNA sequence that may occur due to incorrect incorporation of nucleotide base or bases during replication or transcription or as a result of environmental factors such as UV light, radiations or mutagens. The mutation may be of different types:

• Missense mutation: It is a point mutation that occurs when a change in a single nucleotide base of an amino acid occurs. This results in the substitution of one amino acid for another in the protein made by a gene.

• Insertion: An insertion mutation results in the addition of one or a few nucleotides in the DNA. As a result, the DNA sequence becomes longer and the protein made by the gene may not function properly.

• Deletion: A deletion mutation causes the removal of one or a few nucleotides from the DNA sequence. Small deletions may remove one or a few base pairs within a gene, while larger deletions can remove an entire gene or several neighboring genes. The deleted DNA may alter the function of the resulting protein.

• Frameshift mutation: This type of mutation occurs when the addition or loss of DNA bases changes a gene's reading frame. A reading frame consists of groups of 3 bases that each code for one amino acid. A frameshift mutation causes addition or deletion of bases in numbers that are not divisible by three, thereby resulting in a shift in reading frame of the protein.