Question

Mutations can be classified based on either the effect of the mutation on the function of the gene product or the location of the mutation within the chromosomes. Explain the difference.

Answer 1

Effect of the mutation on the function of the gene product: This type of mutation comes under gene mutation, here a single nucleotide gets changed or deleted from a segment of DNA. Gene mutation may occur because of base substitution or frame shift mutation. Frame shift mutation results in a drastic change because the whole reading frame of nucleotides is changed. Base substitution mutation may be:

• Silent mutation: Occurs when any nucleotide gets changed into another nucleotide but the codon also codes for same amino acids due to degeneracy of genetic code.
• Same sense mutation: Nucleotide gets changed into another nucleotide but the changed codon codes for the amino acid which belongs to the same group of amino acid of previous codon hence genotypic changes will occur but mutation will not be expressed.
• Mis sense mutation: Here a single change in nucleotide changes the codon and a diferent amino acid is coded. For example Sickle cell anaemia in which glutamic acid is replaced by valine amino acid.
• Non sense mutation: Change in nucleotide results in stop codon as a result functional protein is not synthesized as a result mutation will be expressed.

Location of the mutation within the chromosomes: This type of mutation comes under genomatic mutation, here any change in the structure of chromosome or the number of genes present on the chromosome is regarded as structural aberration or chromosomal aberration. They may be because of:

• Addition or duplication: Any gene gets replicated or inserted in the chromosome .
• Deletion: In this type, any gene or segment of a chromosome breaks down from the chromosome and gets deleted from the chromosome. Deletion mutation may be lethal.
• Inversion: In this type a part of DNA segement breaks as a result it may be paracentric inversion (centromere not involved and arm ratio does not change) or pericentric inversion (centromere involved and arm ratio changed).