Question

What are silent mutations? From your knowledge of the genetic code, why do you think most silent mutations affect the third position in a codon. Provide your answer with the 64 universal genetic code table.

Answer 1

##### Answer and Explanation #####

   Mutations-   Mutations are the sudden changes in the gene that lead to the variations in the genotypic and phenotypic characters. It can result a positive control or negative control.

                       Or in Molecular level- These are the nucleotide alternation the nitrogenous bases (A, G, T, C and U) which are responsible to code the various amino acids , after mutation the mutated amino acid can or cannot be same amino acid coding sequence.

     Case of mutation can be in small scale(Base substitution, Insertion, deletion) or large scale( translocation, transversion , cross over of non-homologous chromosomes).

Silent Mutation- This is the type of small scale type of mutation, although it changes genetic codes but does not change any kind of phenotypic characters.

In this case of mutation the codons do change but the amino acid does not change (i.e. XXX codes for Alanine, and after mutation XXZ will also code for Alanine), this is slightly different from neutral mutation in which the codons and amino acid change but the property of the amino acid does not change. (i.e. If XXX codes for Lysine, and after mutation XYX will code for Arginine. Here amino acid changed but the property i.e. Basic does not change of both the amino acids).

Why, In silent mutation the third codon is changed-

As we know that there are 20 amino acids which are code by 64 triplet codons , out of 20 amino acids some have single triplet of codons but some have 2-6 triplet of codons, Since , There is a frequency of the codons to form proteins by coding the amino acids but it is no the strict relationship, the main variation occurs at the third position in case of multiple codons. This is the reason that in some amino acids , if third position is changed that doesn’t lead to change in the certain coding amino acid.

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